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Zhang J, Pei Y, Yi Q, Chen Y, Zhang T, Shi W. Particulate and water-mobilizable phosphorus from a watershed with a plain river network contributes equal amounts of algal available phosphorus to its downstream lake. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 932:173047. [PMID: 38723957 DOI: 10.1016/j.scitotenv.2024.173047] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/30/2023] [Revised: 05/05/2024] [Accepted: 05/06/2024] [Indexed: 05/13/2024]
Abstract
This research was designed to estimate the contributions of phosphorus (P) in different factions from an upstream plain river network to algal growth in a downstream shallow eutrophic lake, Taihu Lake, in China. During three flow regimes, the P fractions in multiple phases (particulate, colloidal and dissolved phases) and their algal availabilities were assessed via bioassays with Dolichospermum flos-aquae as the test organism. The P partitioning patterns among multiple phases were strongly affected by the concentration of total suspended solids (TSS) that changed with the river flow regime, with stronger disturbance of sediments at lower water levels (low flow) and weaker disturbance of sediments at higher water levels (high flow) in the plain river network. The median TSS concentration across the river network decreased from 157.4 mg/L during low flow to 31.8 mg/L during high flow, and the median particulate P concentration decreased from 0.132 mg/L to 0.093 mg/L. The particulate P contributed equally to the amount of algal available P (AAP) as did the water-mobilizable P (colloidal plus dissolved phase) in the rivers flowing into Taihu Lake. The annual average concentrations of particulate algal available P (P-AAP), colloidal algal available P (C-AAP) and dissolved algal available P (D-AAP) were estimated to be 0.032 mg/L, 0.012 mg/L and 0.019 mg/L, respectively, during 2012-2018, accounting for 50.8 %, 19.0 % and 30.2 %, respectively, of the total AAP. At the watershed scale, controlling P drainage from downstream urbanized areas should be emphasized. Additionally, controlling sediment resuspension or reducing the TSS concentration in the inflowing rivers is important for decreasing the particulate P flux to downstream lakes.
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Affiliation(s)
- Jin Zhang
- School of Civil Engineering, Yantai University, Yantai 264005, China
| | - Yu Pei
- School of Civil Engineering, Yantai University, Yantai 264005, China
| | - Qitao Yi
- School of Civil Engineering, Yantai University, Yantai 264005, China.
| | - Yihan Chen
- School of Civil Engineering, Yantai University, Yantai 264005, China; School of Earth and Environment, Anhui University of Science and Technology, Huainan 232001, China
| | - Tao Zhang
- Nanjing Institute of Environmental Sciences, Ministry of Ecology and Environment of the People's Republic of China, Nanjing 210042, China
| | - Wenqing Shi
- School of Environmental Science and Engineering, Nanjing University of Information Science & Technology, Nanjing 210044, China
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2
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He Y, Bond-Lamberty B, Myers-Pigg AN, Newcomer ME, Ladau J, Holmquist JR, Brown JB, Falco N. Effects of spatial variability in vegetation phenology, climate, landcover, biodiversity, topography, and soil property on soil respiration across a coastal ecosystem. Heliyon 2024; 10:e30470. [PMID: 38726202 PMCID: PMC11079102 DOI: 10.1016/j.heliyon.2024.e30470] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2023] [Revised: 03/21/2024] [Accepted: 04/26/2024] [Indexed: 05/12/2024] Open
Abstract
Coastal terrestrial-aquatic interfaces (TAIs) are crucial contributors to global biogeochemical cycles and carbon exchange. The soil carbon dioxide (CO2) efflux in these transition zones is however poorly understood due to the high spatiotemporal dynamics of TAIs, as various sub-ecosystems in this region are compressed and expanded by complex influences of tides, changes in river levels, climate, and land use. We focus on the Chesapeake Bay region to (i) investigate the spatial heterogeneity of the coastal ecosystem and identify spatial zones with similar environmental characteristics based on the spatial data layers, including vegetation phenology, climate, landcover, diversity, topography, soil property, and relative tidal elevation; (ii) understand the primary driving factors affecting soil respiration within sub-ecosystems of the coastal ecosystem. Specifically, we employed hierarchical clustering analysis to identify spatial regions with distinct environmental characteristics, followed by the determination of main driving factors using Random Forest regression and SHapley Additive exPlanations. Maximum and minimum temperature are the main drivers common to all sub-ecosystems, while each region also has additional unique major drivers that differentiate them from one another. Precipitation exerts an influence on vegetated lands, while soil pH value holds importance specifically in forested lands. In croplands characterized by high clay content and low sand content, the significant role is attributed to bulk density. Wetlands demonstrate the importance of both elevation and sand content, with clay content being more relevant in non-inundated wetlands than in inundated wetlands. The topographic wetness index significantly contributes to the mixed vegetation areas, including shrub, grass, pasture, and forest. Additionally, our research reveals that dense vegetation land covers and urban/developed areas exhibit distinct soil property drivers. Overall, our research demonstrates an efficient method of employing various open-source remote sensing and GIS datasets to comprehend the spatial variability and soil respiration mechanisms in coastal TAI. There is no one-size-fits-all approach to modeling carbon fluxes released by soil respiration in coastal TAIs, and our study highlights the importance of further research and monitoring practices to improve our understanding of carbon dynamics and promote the sustainable management of coastal TAIs.
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Affiliation(s)
- Yinan He
- Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720-8126, USA
| | - Ben Bond-Lamberty
- Joint Global Change Research Institute, Pacific Northwest National Laboratory, College Park, MD, 20740, USA
| | - Allison N. Myers-Pigg
- Marine and Coastal Research Laboratory, Pacific Northwest National Laboratory, Sequim, WA, 98382, USA
- Department of Environmental Sciences, University of Toledo, Toledo, OH, 43606, USA
| | - Michelle E. Newcomer
- Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720-8126, USA
| | - Joshua Ladau
- Computational Biosciences Group, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA
| | - James R. Holmquist
- Smithsonian Environmental Research Center, 647 Contees Wharf Road, Edgewater, MD, 21037, USA
| | - James B. Brown
- Computational Biosciences Group, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720, USA
| | - Nicola Falco
- Earth and Environmental Sciences Area, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Berkeley, CA, 94720-8126, USA
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Cravotta CA, Tasker TL, Smyntek PM, Blomquist JD, Clune JW, Zhang Q, Schmadel NM, Schmer NK. Legacy sediment as a potential source of orthophosphate: Preliminary conceptual and geochemical models for the Susquehanna River, Chesapeake Bay watershed, USA. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 912:169361. [PMID: 38104826 DOI: 10.1016/j.scitotenv.2023.169361] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Revised: 11/28/2023] [Accepted: 12/11/2023] [Indexed: 12/19/2023]
Abstract
Nutrient pollution from agriculture and urban areas plus acid mine drainage (AMD) from legacy coal mines are primary causes of water-quality impairment in the Susquehanna River, which is the predominant source of freshwater and nutrients entering the Chesapeake Bay. Recent increases in the delivery of dissolved orthophosphate (PO4) from the river to the bay may be linked to long-term increases in pH, decreased acidity of precipitation, and decreased acidity, iron, and aluminum loading from widespread AMD. Since the 1950s, baseline pH increased from ~6.5 to ~8 in the West Branch and "North Branch" of the Susquehanna River, which drain bituminous and anthracite coalfields of Pennsylvania. A current baseline pH of ~8 and daily maxima exceeding 9 have been documented along the lower Susquehanna River. In response to improved river quality, bioavailable PO4 now may be released into solution from legacy sediment that has filled major impoundments in lower reaches of the river. At typical pH (5-8) of natural water, aqueous PO4 species tend to be adsorbed by hydrous iron, aluminum, and manganese oxides that coat soil and sediment particles; however, PO4 may be substantially desorbed at pH >8. We created a geochemical model that simulates equilibrium aqueous/solid distributions of PO4 as pH and other solution characteristics change. Considering current conditions in the lower Susquehanna River, the model demonstrates potential for extensive release of adsorbed PO4 at pH >8. Empirical data from laboratory experiments corroborate model results. The transfer of PO4 into the water column may increase algae growth, which removes CO2 and drives pH to higher values, facilitating additional PO4 release and exacerbating the potential for harmful algal blooms. Thus, legacy sediment is a currently unquantified source of PO4 that warrants consideration by resource managers and programs collaborating to reduce phosphorus loads to the bay and similar settings worldwide.
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Affiliation(s)
- Charles A Cravotta
- U.S. Geological Survey, Pennsylvania Water Science Center, New Cumberland, PA, United States of America.
| | - Travis L Tasker
- Saint Francis University, Loretto, PA, United States of America
| | - Peter M Smyntek
- Saint Vincent College, Latrobe, PA, United States of America
| | - Joel D Blomquist
- U.S. Geological Survey, Maryland-Delaware-District of Columbia Water Science Center, Catonsville, MD, United States of America
| | - John W Clune
- U.S. Geological Survey, Pennsylvania Water Science Center, Williamsport, PA, United States of America
| | - Qian Zhang
- University of Maryland Center for Environmental Science, USEPA Chesapeake Bay Program, Annapolis, MD, United States of America
| | - Noah M Schmadel
- U.S. Geological Survey, Oregon Water Science Center, Portland, OR, United States of America
| | - Natalie K Schmer
- U.S. Geological Survey, Pennsylvania Water Science Center, Bridgeville, PA, United States of America
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Barathan BP, Chen W, Su Y, Wang X, Chen Y. The effects of nutrient loading from different sources on eutrophication in a large shallow lake in Southeast China. ENVIRONMENTAL GEOCHEMISTRY AND HEALTH 2023; 45:7603-7620. [PMID: 37395908 DOI: 10.1007/s10653-023-01641-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 05/31/2023] [Indexed: 07/04/2023]
Abstract
Lake water eutrophication has become one of the leading obstacles to sustainable economic development in China. Research on the effects of mainstream currents on reservoirs has been relatively underdeveloped compared with research on tributaries, though changes in the water-sediment transport regime in a downstream river may affect nutrient transport behavior in a lake connected to that river. This is particularly problematic because certain wastewater sources, including runoff from agricultural wastes and industrial discharges, adversely affect lake water. Our study focused on Sanshiliujiao Lake, a significant drinking water source in Fujian, Southeast China, that has suffered considerably from eutrophication over the past few decades. This study aimed to estimate the phosphorus and nitrogen loads to the lake, exploring their sources and their ecologic effects using in situ observation and the export coefficient model. Our results showed that the pollution loads of total phosphorus (TP) and total nitrogen (TN) were 2.390 and 46.040 t/year, respectively, most of which were derived from the water diversion (TP 45.7%, TN 29.2%) and non-point source (TP 30.2%, TN 41.6%). The TN input was the highest in East river (3.557 kg/d), followed by Red river (2.524 kg/d). During the wet season, the input of TP and TN increased by 14.6 and 18.7 times, respectively, but produced only slight variations in concentration. Water diversion enriched the nutrients inputs and altered the structure and abundance of phytoplankton communities. In addition, when water flows from the main river directly to Sanshiliujiao Lake, algal blooms in river-connected lakes are significantly exacerbated, so our study may also serve as a theoretical basis to regulate eutrophication in Sanshiliujiao Lake.
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Affiliation(s)
- Balaji-Prasath Barathan
- Environmental Science and Engineering College, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, 350007, People's Republic of China
- Fujian Province Research Centre for River and Lake Health Assessment, Fuzhou, 350007, People's Republic of China
| | - Wenting Chen
- Environmental Science and Engineering College, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, 350007, People's Republic of China
| | - Yuping Su
- Environmental Science and Engineering College, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, 350007, People's Republic of China.
- Fujian Province Research Centre for River and Lake Health Assessment, Fuzhou, 350007, People's Republic of China.
| | - Xue Wang
- Environmental Science and Engineering College, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, 350007, People's Republic of China
| | - Yinxing Chen
- Environmental Science and Engineering College, Fujian Key Laboratory of Pollution Control and Resource Recycling, Fujian Normal University, Fuzhou, 350007, People's Republic of China
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5
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Kua ZX, Davis CM, Townley LA, Stella JC, Shaw SB. Analyzing the impact of agricultural BMPs on stream nutrient load and biotic health in the Susquehanna-Chemung basin of New York. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2023; 335:117521. [PMID: 36870193 DOI: 10.1016/j.jenvman.2023.117521] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2022] [Revised: 02/08/2023] [Accepted: 02/13/2023] [Indexed: 06/18/2023]
Abstract
Despite the widespread use of agricultural best management practices (BMPs) to reduce watershed scale nutrient loads, there remain few studies that use directly observed data - instead of models - to evaluate BMP effectiveness at the watershed scale. In this study, we make use of extensive ambient water quality data, stream biotic health data, and BMP implementation data within the New York State portion of the Chesapeake Bay watershed to assess the role of BMPs on reducing nutrient loads and modifying biotic health in major rivers. The specific BMPs considered were riparian buffers and nutrient management planning. A simple mass balance approach was used to evaluate the role of wastewater treatment plant nutrient reductions, agricultural land use changes, and these two agricultural BMPs in matching observed downward trends in nutrient load. In the Eastern nontidal network (NTN) catchment - where BMPs have been more widely reported - the mass balance model suggested a small but discernible contribution of BMPs in matching the observed downward trend in total phosphorus. Contrastingly, BMP implementations did not show clear contributions towards total nitrogen reductions in the Eastern NTN catchment nor for the total nitrogen and phosphorus in the Western NTN catchment, where BMP implementation data are more limited. Assessment of the relationship between stream biotic health and BMP implementation using regression models found limited connection between extent of BMP implementation and biotic health. In this case, however, spatiotemporal mismatches between the datasets and the relatively stable biotic health, typically of moderate to good quality even before BMP implementation, may reflect the need for better monitoring design to assess BMP effects at the subwatershed scale. Additional studies, perhaps using citizen scientists, may be able to provide more suitable data within the existing frameworks of the long-term surveys. Given the preponderance of studies that rely only on modeling to understand nutrient loading reductions achieved by implementation of BMPs, it is essential to continue to collect empirical data to meaningfully evaluate whether there are actual measurable changes due to BMPs.
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Affiliation(s)
- Zi Xun Kua
- Department of Sustainable Resources Management, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY, 13210, USA
| | - Cassandra M Davis
- Division of Water, Bureau of Water Resource Management, 625 Broadway, 4th Floor, Albany, NY, 12233-3508, USA
| | - Lauren A Townley
- Division of Water, Bureau of Water Resource Management, 625 Broadway, 4th Floor, Albany, NY, 12233-3508, USA
| | - John C Stella
- Department of Sustainable Resources Management, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY, 13210, USA
| | - Stephen B Shaw
- Department of Environmental Resources Engineering, State University of New York College of Environmental Science and Forestry, 1 Forestry Drive, Syracuse, NY, 13210, USA.
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6
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Zhang Q, Fisher TR, Buchanan C, Gustafson AB, Karrh RR, Murphy RR, Testa JM, Tian R, Tango PJ. Nutrient limitation of phytoplankton in three tributaries of Chesapeake Bay: Detecting responses following nutrient reductions. WATER RESEARCH 2022; 226:119099. [PMID: 36302271 DOI: 10.1016/j.watres.2022.119099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Revised: 09/08/2022] [Accepted: 09/09/2022] [Indexed: 06/16/2023]
Abstract
Many coastal ecosystems suffer from eutrophication, algal blooms, and dead zones due to excessive anthropogenic inputs of nitrogen (N) and phosphorus (P). This has led to regional restoration efforts that focus on managing watershed loads of N and P. In Chesapeake Bay, the largest estuary in the United States, dual nutrient reductions of N and P have been pursued since the 1980s. However, it remains unclear whether nutrient limitation - an indicator of restriction of algal growth by supplies of N and P - has changed in the tributaries of Chesapeake Bay following decades of reduction efforts. Toward that end, we analyzed historical data from nutrient-addition bioassay experiments and data from the Chesapeake Bay long-term water-quality monitoring program for six stations in three tidal tributaries (i.e., Patuxent, Potomac, and Choptank Rivers). Classification and regression tree (CART) models were developed using concurrent collections of water-quality parameters for each bioassay monitoring location during 1990-2003, which satisfactorily predicted the bioassay-based measures of nutrient limitation (classification accuracy = 96%). Predictions from the CART models using water-quality monitoring data showed enhanced nutrient limitation over the period of 1985-2020 at four of the six stations, including the downstream station in each of these three tributaries. These results indicate detectable, long-term water-quality improvements in the tidal tributaries. Overall, this research provides a new analytical tool for detecting signs of ecosystem recovery following nutrient reductions. More broadly, the approach can be adapted to other waterbodies with long-term bioassays and water-quality data sets to detect ecosystem recovery.
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Affiliation(s)
- Qian Zhang
- University of Maryland Center for Environmental Science / Chesapeake Bay Program, 1750 Forest Drive, Suite 130, Annapolis, MD 21401, USA.
| | - Thomas R Fisher
- Horn Point Laboratory, University of Maryland Center for Environmental Science, 2020 Horns Point Rd, Cambridge, MD 21613, USA
| | - Claire Buchanan
- Interstate Commission on the Potomac River Basin, 30 West Gude Drive, Suite 450, Rockville, MD 20850, USA
| | - Anne B Gustafson
- Horn Point Laboratory, University of Maryland Center for Environmental Science, 2020 Horns Point Rd, Cambridge, MD 21613, USA
| | - Renee R Karrh
- Maryland Department of Natural Resources, 580 Taylor Ave, Annapolis, MD 21401, USA
| | - Rebecca R Murphy
- University of Maryland Center for Environmental Science / Chesapeake Bay Program, 1750 Forest Drive, Suite 130, Annapolis, MD 21401, USA
| | - Jeremy M Testa
- Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, 146 Williams Street, Solomons, MD 20688, USA
| | - Richard Tian
- University of Maryland Center for Environmental Science / Chesapeake Bay Program, 1750 Forest Drive, Suite 130, Annapolis, MD 21401, USA
| | - Peter J Tango
- U.S. Geological Survey / Chesapeake Bay Program, 1750 Forest Drive, Suite 130, Annapolis, MD 21401, USA
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Xie H, Gao T, Wan N, Xiong Z, Dong J, Lin C, Lai X. Controls for multi-temporal patterns of riverine nitrogen and phosphorus export to lake: Implications for catchment management by high-frequency observations. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2022; 320:115858. [PMID: 36056487 DOI: 10.1016/j.jenvman.2022.115858] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2022] [Revised: 07/22/2022] [Accepted: 07/22/2022] [Indexed: 06/15/2023]
Abstract
Intensifying human activity coupled with climate change increase the transport of excess riverine nitrogen (N) and phosphorus (P) loading from catchment to lake, leading to eutrophication and harmful algal blooms worldwide. To improve understanding of multi-temporal patterns of riverine N and P export and their hydro-biogeochemical controls over both episodic events and long-term trend, we analyzed and interpreted high-frequency data of total nitrogen (TN), ammonia-nitrogen (NH4-N), and total phosphorus (TP) provided by an automatic water quality monitoring station in a typical agricultural catchment draining to Lake Chaohu, China. Mann-Kendall test revealed a significant decreasing trend of riverine N and P concentration most of the time during 2018-2020. At the sub-daily scale, intraday TN concentrations varied by more than 1 mg/L in 31.8% of the period. Monthly TN and TP concentrations were particularly high in December 2019, indicating combined effect of hydrologic (long dry antecedent period and subsequent intensive rainfall events) and anthropogenic controls (fertilization and agricultural drainage). Significantly higher TN concentrations in winter and TP concentrations in summer reflected coupled dominances of precipitation and temperature on hydrologic and biogeochemical processes. Rainfall events with very heavy intensity drove disproportionate N and P loads (more than 20% of the total export) in only 3.2% of the period. Moderate and very heavy events registered the highest TN and TP concentrations, respectively. Our results highlighted the importance of automatic water quality monitoring station to reveal dynamics of riverine N and P export, which may imply future nutrient loading abatement plans for lake-connected catchment.
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Affiliation(s)
- Hui Xie
- Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China
| | - Tiantian Gao
- Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China; Collaborative Innovation Center on Forecast and Evaluation of Meteorological Disasters, School of Applied Meteorology, Nanjing University of Information Science and Technology, Nanjing, 210044, China
| | - Nengsheng Wan
- Institute of Lake Ecology and Environment, Chaohu Lake Bureau of Anhui Province, Hefei, 238000, China
| | - Zhuyang Xiong
- Institute of Lake Ecology and Environment, Chaohu Lake Bureau of Anhui Province, Hefei, 238000, China
| | - Jianwei Dong
- School of Marine Science and Engineering, Nanjing Normal University, Nanjing, 210023, China
| | - Chen Lin
- Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China
| | - Xijun Lai
- Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, Nanjing, 210008, China.
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Sabo RD, Sullivan B, Wu C, Trentacoste E, Zhang Q, Shenk GW, Bhatt G, Linker LC. Major point and nonpoint sources of nutrient pollution to surface water have declined throughout the Chesapeake Bay watershed. ENVIRONMENTAL RESEARCH COMMUNICATIONS 2022; 4:1-11. [PMID: 37089436 PMCID: PMC10116850 DOI: 10.1088/2515-7620/ac5db6] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Understanding drivers of water quality in local watersheds is the first step for implementing targeted restoration practices. Nutrient inventories can inform water quality management decisions by identifying shifts in nitrogen (N) and phosphorus (P) balances over space and time while also keeping track of the likely urban and agricultural point and nonpoint sources of pollution. The Chesapeake Bay Program's Chesapeake Assessment Scenario Tool (CAST) provides N and P balance data for counties throughout the Chesapeake Bay watershed, and these data were leveraged to create a detailed nutrient inventory for all the counties in the watershed from 1985-2019. This study focuses on three primary watershed nutrient balance components-agricultural surplus, atmospheric deposition, and point source loads-which are thought to be the leading anthropogenic drivers of nutrient loading trends across the watershed. All inputs, outputs, and derived metrics (n=53) like agricultural surplus and nutrient use efficiency, were subjected to short- and long-term trend analyses to discern how sources of pollution to surface water have changed over time. Across the watershed from 1985-2019, downward trends in atmospheric deposition were ubiquitous. Though there are varying effects, long-term declines in agricultural surplus were observed, likely because nutrients are being managed more efficiently. Multiple counties' point source loads declined, primarily associated with upgrades at major cities that discharge treated wastewater directly to tidal waters. Despite all of these positive developments, recent increases in agricultural surpluses from 2009-2019 highlight that water quality gains may soon be reversed in many agricultural areas of the basin. Besides tracking progress and jurisdictional influence on pollution sources, the nutrient inventory can be used for retrospective water quality analysis to highlight drivers of past improvement/degradation of water quality trends and for decision makers to develop and track their near- and long-term watershed restoration strategies.
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Affiliation(s)
- Robert D Sabo
- U.S. Environmental Protection Agency, Office of Research and Development, Center for Public Health and Environmental Assessment, Washington, DC, United States of America
| | - Breck Sullivan
- U.S. Geological Survey, Chesapeake Research Consortium, Chesapeake Bay Program Office, Annapolis, MD, United States of America
| | - Cuiyin Wu
- ERT, Inc., Laurel, MD, United States of America
| | - Emily Trentacoste
- U.S. Environmental Protection Agency, Office of Research and Development, Immediate Office of the Assistant Administrator, Washington, DC, United States of America
| | - Qian Zhang
- University of Maryland Center for Environmental Science, Chesapeake Bay Program Office, Annapolis, MD, United States of America
| | - Gary W Shenk
- U.S. Geological Survey, Chesapeake Bay Program Office, Annapolis, MD, United States of America
| | - Gopal Bhatt
- Pennsylvania State University, Chesapeake Bay Program Office, Annapolis, MD, United States of America
| | - Lewis C Linker
- U.S. Environmental Protection Agency, Office of Research and Development, Immediate Office of the Assistant Administrator, Washington, DC, United States of America
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9
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Frei RJ, Lawson GM, Norris AJ, Cano G, Vargas MC, Kujanpää E, Hopkins A, Brown B, Sabo R, Brahney J, Abbott BW. Limited progress in nutrient pollution in the U.S. caused by spatially persistent nutrient sources. PLoS One 2021; 16:e0258952. [PMID: 34843503 PMCID: PMC8629290 DOI: 10.1371/journal.pone.0258952] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2021] [Accepted: 10/10/2021] [Indexed: 01/01/2023] Open
Abstract
Human agriculture, wastewater, and use of fossil fuels have saturated ecosystems with nitrogen and phosphorus, threatening biodiversity and human water security at a global scale. Despite efforts to reduce nutrient pollution, carbon and nutrient concentrations have increased or remained high in many regions. Here, we applied a new ecohydrological framework to ~12,000 water samples collected by the U.S. Environmental Protection Agency from streams and lakes across the contiguous U.S. to identify spatial and temporal patterns in nutrient concentrations and leverage (an indicator of flux). For the contiguous U.S. and within ecoregions, we quantified trends for sites sampled repeatedly from 2000 to 2019, the persistence of spatial patterns over that period, and the patch size of nutrient sources and sinks. While we observed various temporal trends across ecoregions, the spatial patterns of nutrient and carbon concentrations in streams were persistent across and within ecoregions, potentially because of historical nutrient legacies, consistent nutrient sources, and inherent differences in nutrient removal capacity for various ecosystems. Watersheds showed strong critical source area dynamics in that 2-8% of the land area accounted for 75% of the estimated flux. Variability in nutrient contribution was greatest in catchments smaller than 250 km2 for most parameters. An ensemble of four machine learning models confirmed previously observed relationships between nutrient concentrations and a combination of land use and land cover, demonstrating how human activity and inherent nutrient removal capacity interactively determine nutrient balance. These findings suggest that targeted nutrient interventions in a small portion of the landscape could substantially improve water quality at continental scales. We recommend a dual approach of first prioritizing the reduction of nutrient inputs in catchments that exert disproportionate influence on downstream water chemistry, and second, enhancing nutrient removal capacity by restoring hydrological connectivity both laterally and vertically in stream networks.
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Affiliation(s)
- Rebecca J. Frei
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
- Department of Renewable Resources, University of Alberta, Edmonton, Alberta, Canada
| | - Gabriella M. Lawson
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Adam J. Norris
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Gabriel Cano
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Maria Camila Vargas
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Elizabeth Kujanpää
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Austin Hopkins
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Brian Brown
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Robert Sabo
- United States Environmental Protection Agency, Washington, D. C., United States of America
| | - Janice Brahney
- Department of Watershed Sciences and Ecology Center, Utah State University, Logan, Utah, United States of America
| | - Benjamin W. Abbott
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
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10
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He J, Christakos G, Wu J, Li M, Leng J. Spatiotemporal BME characterization and mapping of sea surface chlorophyll in Chesapeake Bay (USA) using auxiliary sea surface temperature data. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 794:148670. [PMID: 34225143 DOI: 10.1016/j.scitotenv.2021.148670] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/29/2021] [Revised: 06/20/2021] [Accepted: 06/21/2021] [Indexed: 06/13/2023]
Abstract
Improving the spatiotemporal coverage of remote sensing (RS) products, such as sea surface chlorophyll concentration (SSCC), can offer a better understanding of the spatiotemporal SSCC distribution for ocean management purposes. In the first part of this work, 834 in-situ SSCC measurements of the SeaBASS-NASA (National Aeronautics and Space Administration) during 2002-2016 served as the empirical dataset. A moving window with ±3 days and ±0.5° centered at each of the in-situ SSCC measurements established a search neighborhood for Moderate Resolution Imaging Spectroradiometer Level 2 (MODIS L2) SSCC and MODIS L2 sea surface temperature (SST) data, and the matched SSCC and SST data were used for building a linear SSCC-SST relationship. The unmatched SST was introduced to the linear model for generating soft SSCC data with uniform distributions. The inherent spatiotemporal dependency of the SSCC distribution was then represented by the Bayesian maximum entropy (BME) method, which incorporated the soft SSCC data as auxiliary variable for SSCC estimation and mapping purposes. The results showed that a 75.3% accuracy improvement of remote SSCC retrieval in terms of R2 can be achieved by BME-based method compared to the original MODIS L2 product. Subsequently, the BME-based method was applied to obtain daily SSCC dataset in Chesapeake Bay (USA) during the period 2010-2019. It was found that the SSCC distribution exhibited a decreasing spatial trend from the upper bay to the outer bay, whereas decreasing and increasing temporal trends were detected during the periods 2011-2014 and 2016-2019, respectively. The generalized Cauchy process was used to quantitatively describe the autocorrelation SSCC function in the Chesapeake Bay. The results showed that the outer bay exhibited the strongest long-range dependence among the four sub-regions, whereas the middle bay exhibited the weakest long-range dependence. Finally, one-point and two-point stochastic site indicators (SSIs) were employed to explore the spatiotemporal SSCC characteristics in Chesapeake Bay. The one-point SSI results showed that nearly 100% of the upper, middle and the lower bay areas experienced a high SSCC level (>5 mg/m3) during the entire study period. The area with SSCC >5 mg/m3 in the outer bay increased a lot during the winter season, but the area with SSCC >10 or 20 mg/m3 decreased significantly in the upper, middle and lower bay. Simultaneously, the SSCC dispersion in these areas was rather small during the winter season. On the other hand, the two-point SSI results showed that although the SSCC levels differ among the four sub-regions, but the SSCC connectivity structures between pairs of points also displayed some similarities in terms of their spatiotemporal dependency. In conclusion, the proposed BME-based method was shown to be a promising remote SSCC mapping technique that exhibited a powerful ability to improve both accuracy and coverage of RS products. The SSIs can be also used to explore the spatiotemporal characteristics of a variety of natural attributes in waters.
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Affiliation(s)
- Junyu He
- Ocean Academy, Zhejiang University, Zhoushan 316021, P. R. China; Ocean College, Zhejiang University, Zhoushan 316021, P. R. China
| | - George Christakos
- Ocean College, Zhejiang University, Zhoushan 316021, P. R. China; Department of Geography, San Diego State University, San Diego 92182-4493, USA.
| | - Jiaping Wu
- Ocean Academy, Zhejiang University, Zhoushan 316021, P. R. China; Ocean College, Zhejiang University, Zhoushan 316021, P. R. China
| | - Ming Li
- Ocean College, Zhejiang University, Zhoushan 316021, P. R. China; East China Normal University, Shanghai 200062, P. R. China
| | - Jianxing Leng
- Ocean Academy, Zhejiang University, Zhoushan 316021, P. R. China; Ocean College, Zhejiang University, Zhoushan 316021, P. R. China
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11
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Jones EF, Frei RJ, Lee RM, Maxwell JD, Shoemaker R, Follett AP, Lawson GM, Malmfeldt M, Watts R, Aanderud ZT, Allred C, Asay AT, Buhman M, Burbidge H, Call A, Crandall T, Errigo I, Griffin NA, Hansen NC, Howe JC, Meadows EL, Kujanpaa E, Lange L, Nelson ML, Norris AJ, Ostlund E, Suiter NJ, Tanner K, Tolworthy J, Vargas MC, Abbott BW. Citizen science reveals unexpected solute patterns in semiarid river networks. PLoS One 2021; 16:e0255411. [PMID: 34411107 PMCID: PMC8376020 DOI: 10.1371/journal.pone.0255411] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/01/2021] [Accepted: 07/15/2021] [Indexed: 11/18/2022] Open
Abstract
Human modification of water and nutrient flows has resulted in widespread degradation of aquatic ecosystems. The resulting global water crisis causes millions of deaths and trillions of USD in economic damages annually. Semiarid regions have been disproportionately affected because of high relative water demand and pollution. Many proven water management strategies are not fully implemented, partially because of a lack of public engagement with freshwater ecosystems. In this context, we organized a large citizen science initiative to quantify nutrient status and cultivate connection in the semiarid watershed of Utah Lake (USA). Working with community members, we collected samples from ~200 locations throughout the 7,640 km2 watershed on a single day in the spring, summer, and fall of 2018. We calculated ecohydrological metrics for nutrients, major ions, and carbon. For most solutes, concentration and leverage (influence on flux) were highest in lowland reaches draining directly to the lake, coincident with urban and agricultural sources. Solute sources were relatively persistent through time for most parameters despite substantial hydrological variation. Carbon, nitrogen, and phosphorus species showed critical source area behavior, with 10-17% of the sites accounting for most of the flux. Unlike temperate watersheds, where spatial variability often decreases with watershed size, longitudinal variability showed an hourglass shape: high variability among headwaters, low variability in mid-order reaches, and high variability in tailwaters. This unexpected pattern was attributable to the distribution of human activity and hydrological complexity associated with return flows, losing river reaches, and diversions in the tailwaters. We conclude that participatory science has great potential to reveal ecohydrological patterns and rehabilitate individual and community relationships with local ecosystems. In this way, such projects represent an opportunity to both understand and improve water quality in diverse socioecological contexts.
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Affiliation(s)
- Erin Fleming Jones
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Rebecca J. Frei
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Raymond M. Lee
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Jordan D. Maxwell
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Rhetta Shoemaker
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Andrew P. Follett
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Gabriella M. Lawson
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Madeleine Malmfeldt
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Rachel Watts
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Zachary T. Aanderud
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Carter Allred
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Allison Tuttle Asay
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Madeline Buhman
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Hunter Burbidge
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Amber Call
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Trevor Crandall
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Isabella Errigo
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Natasha A. Griffin
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Neil C. Hansen
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Jansen C. Howe
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Emily L. Meadows
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Elizabeth Kujanpaa
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Leslie Lange
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Monterey L. Nelson
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Adam J. Norris
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Elysse Ostlund
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Nicholas J. Suiter
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Kaylee Tanner
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Joseph Tolworthy
- Department of Geology, Brigham Young University, Provo, Utah, United States of America
| | - Maria Camila Vargas
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
| | - Benjamin W. Abbott
- Department of Plant and Wildlife Sciences, Brigham Young University, Provo, Utah, United States of America
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12
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Bos J, Williams M, Smith D, Armstrong S, Harmel D. Long-term effect of poultry litter application on phosphorus balances and runoff losses. JOURNAL OF ENVIRONMENTAL QUALITY 2021; 50:639-652. [PMID: 33742467 DOI: 10.1002/jeq2.20219] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2020] [Accepted: 03/12/2021] [Indexed: 06/12/2023]
Abstract
Assessment of annual and cumulative impacts of phosphorus (P) management strategies at field and watershed scales is needed to improve crop use efficiency and minimize environmental impacts. The objectives of this study were (a) to assess relationships among P balance, soil test P (STP) concentration, and runoff dissolved reactive P (DRP) concentration from fields receiving different poultry litter application rates (0.0-13.4 Mg ha-1 ) and (b) to determine the effect of long-term poultry litter application to fields on watershed DRP loss. Nutrient management practices, crop yield, STP, and runoff losses were assessed from nine fields and two watersheds located near Riesel, TX, from 2000 to 2015. Field-scale P balances were largely controlled by P application rate and exhibited a positive relationship with STP and runoff DRP flow-weighted mean concentration. Using a before-after control-impact experimental design that included monitoring at both field and watershed scales showed the influence of field P management on watershed DRP loss varied according to both source (i.e., P application rate, impacted area) and transport (i.e., hydrological connectivity) factors. Increased risk of watershed DRP loss was observed during wet years and years with two poultry litter applications to fields within the watershed. The percentage of the total watershed area receiving high rates of poultry litter also played a critical role in determining the risk of DRP loss. Findings highlight the impact of long-term P management strategies on DRP loss at both field and watershed scales and show the importance of incorporating hydrologic connectivity when assessing conservation effects on water quality.
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Affiliation(s)
- Janae Bos
- National Soil Erosion Research Lab., USDA-ARS, 275 S Russell Street, West Lafayette, IN, 47907, USA
- Dep. of Agronomy, Purdue Univ., 915 West State Street, West Lafayette, IN, 47907, USA
| | - Mark Williams
- National Soil Erosion Research Lab., USDA-ARS, 275 S Russell Street, West Lafayette, IN, 47907, USA
| | - Douglas Smith
- Grassland Soil and Water Research Lab., USDA-ARS, 808 East Blackland Road, Temple, TX, 76502, USA
| | - Shalamar Armstrong
- Dep. of Agronomy, Purdue Univ., 915 West State Street, West Lafayette, IN, 47907, USA
| | - Daren Harmel
- Center for Agricultural Resources Research Center, USDA-ARS, 2150 Centre Avenue, Fort Collins, CO, 80526, USA
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13
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Sabo RD, Clark CM, Compton JE. Considerations when using nutrient inventories to prioritize water quality improvement efforts across the US. ENVIRONMENTAL RESEARCH COMMUNICATIONS 2021; 3:1-13. [PMID: 36457483 PMCID: PMC9709726 DOI: 10.1088/2515-7620/abf296] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/09/2023]
Abstract
Ongoing water quality degradation tied to nitrogen and phosphorus pollution results in significant economic damages by diminishing the recreational value of surface water and compromising fisheries. Progress in decreasing nitrogen and phosphorus pollution to surface water over the past two decades has been slow. Limited resources need to be leveraged efficiently and effectively to prioritize watersheds for restoration. Leveraging recent nitrogen and phosphorus inventories for the years 2002, 2007, and 2012, we extracted relevant flux and demand terms to help identify US subbasins that are likely contributing a disproportionate amount of point and non-point source nutrient pollution to surface water by exploring the mean spatial distribution of terrestrial anthropogenic surplus, agricultural surplus, agricultural nutrient use efficiency, and point source loads. A small proportion of the landscape, <25% of subbasin area of the United States, contains 50% of anthropogenic and agriculture nitrogen and phosphorus surplus while only 2% of landscape contributes >50% of point source loads into surface water. Point source loads are mainly concentrated in urban areas across the country with point source loading rates often exceeding >10.0 kg N ha-1 yr-1 and >1.0 kg P ha-1 yr-1. However, the ability for future upgrades to wastewater treatment plant infrastructure alone is unlikely to drive further improvement in water quality, outside of local water ways, since point source loads only account for ~4% of anthropogenic N and P surplus. As such, further progress in boosting nutrient use efficiency in agricultural production, usually lowest in areas of intensive livestock production, would likely contribute to the biggest gains to water quality restoration goals. This analysis and the corresponding database integrate multiple streams of information to highlight areas where N and P are being managed inefficiently to give decision makers a succinct platform to identify likely areas and sources of water quality degradation.
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Affiliation(s)
- Robert D Sabo
- Center for Public Health and Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C., United States of America
| | - Christopher M Clark
- Center for Public Health and Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Washington, D.C., United States of America
| | - Jana E Compton
- Center for Public Health and Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency, Corvallis, OR, United States of America
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14
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Sabo RD, Clark CM, Gibbs DA, Metson GS, Todd MJ, LeDuc SD, Greiner D, Fry MM, Polinsky R, Yang Q, Tian H, Compton JE. Phosphorus Inventory for the Conterminous United States (2002-2012). JOURNAL OF GEOPHYSICAL RESEARCH. BIOGEOSCIENCES 2021; 126:1-21. [PMID: 37089664 PMCID: PMC10116864 DOI: 10.1029/2020jg005684] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
Published reports suggest efforts designed to prevent the occurrence of harmful algal blooms and hypoxia by reducing non-point and point source phosphorus (P) pollution are not delivering water quality improvements in many areas. Part of the uncertainty in evaluating watershed responses to management practices is the lack of standardized estimates of phosphorus inputs and outputs. To assess P trends across the conterminous United States, we compiled an inventory using publicly available datasets of agricultural P fluxes, atmospheric P deposition, human P demand and waste, and point source discharges for 2002, 2007, and 2012 at the scale of the 8-digit Hydrologic Unit Code subbasin (~1,800 km2). Estimates of agricultural legacy P surplus accumulated from 1945 to 2001 were also developed. Fertilizer and manure inputs were found to exceed crop removal rates by up to 50% in many agricultural regions. This excess in inputs has led to the continued accumulation of legacy P in agricultural lands. Atmospheric P deposition increased throughout the Rockies, potentially contributing to reported increases in surface water P concentrations in undisturbed watersheds. In some urban areas, P fluxes associated with human waste and non-farm fertilizer use has declined despite population growth, likely due, in part, to various sales bans on P-containing detergents and fertilizers. Although regions and individual subbasins have different contemporary and legacy P sources, a standardized method of accounting for large and small fluxes and ready to use inventory numbers provide essential infromation to coordinate targeted interventions to reduce P concentrations in the nation's waters.
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Affiliation(s)
- Robert D Sabo
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Office of Research and Development, U.S. EPA, Washington, DC, USA
| | - Christopher M Clark
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Office of Research and Development, U.S. EPA, Washington, DC, USA
| | | | - Geneviève S Metson
- Department of Physics, Chemistry, and Biology, Linköping University, Linköping, Sweden
| | - M Jason Todd
- U.S. Environmental Protection Agency, Office of Chemical Safety and Pollution, U.S. EPA, Washington, DC, USA
| | - Stephen D LeDuc
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Office of Research and Development, U.S. EPA, Research Triangle Park, NC, USA
| | - Diana Greiner
- U.S. Environmental Protection Agency, U.S. EPA, Dallas, TX, USA
| | - Meridith M Fry
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Office of Research and Development, U.S. EPA, Washington, DC, USA
| | - Robyn Polinsky
- U.S. Environmental Protection Agency, U.S. EPA, Atlanta, GA, USA
| | - Qichun Yang
- Pacific Northwest National Lab, Richland, WA, USA
| | - Hanqin Tian
- International Center for Climate and Global Change Research, School of Forestry and Wildlife Sciences, Auburn University, Auburn, AL, USA
| | - Jana E Compton
- Center for Public Health and Environmental Assessment, U.S. Environmental Protection Agency, Office of Research and Development, U.S. EPA, Corvallis, OR, USA
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15
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Simpson ZP, McDowell RW, Condron LM, McDaniel MD, Jarvie HP, Abell JM. Sediment phosphorus buffering in streams at baseflow: A meta-analysis. JOURNAL OF ENVIRONMENTAL QUALITY 2021; 50:287-311. [PMID: 33491241 DOI: 10.1002/jeq2.20202] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/06/2020] [Accepted: 01/17/2021] [Indexed: 06/12/2023]
Abstract
Phosphorus (P) pollution of surface waters remains a challenge for protecting and improving water quality. Central to the challenge is understanding what regulates P concentrations in streams. This quantitative review synthesizes the literature on a major control of P concentrations in streams at baseflow-the sediment P buffer-to better understand streamwater-sediment P interactions. We conducted a global meta-analysis of sediment equilibrium phosphate concentrations at net zero sorption (EPC0 ), which is the dissolved reactive P (DRP) concentration toward which sediments buffer solution DRP. Our analysis of 45 studies and >900 paired observations of DRP and EPC0 showed that sediments often have potential to remove or release P to the streamwater (83% of observations), meaning that "equilibrium" between sediment and streamwater is rare. This potential for P exchange is moderated by sediment and stream characteristics, including sorption affinity, stream pH, exchangeable P concentration, and particle sizes. The potential for sediments to modify streamwater DRP concentrations is often not realized owing to other factors (e.g., hydrologic interactions). Sediment surface chemistry, hyporheic exchange, and biota can also influence the potential exchange of P between sediments and the streamwater. Methodological choices significantly influenced EPC0 determination and thus the estimated potential for P exchange; we therefore discuss how to measure and report EPC0 to best suit research objectives and aid in interstudy comparison. Our results enhance understanding of the sediment P buffer and inform how EPC0 can be effectively applied to improve management of aquatic P pollution and eutrophication.
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Affiliation(s)
- Zachary P Simpson
- Faculty of Agriculture and Life Sciences, Lincoln Univ., P.O. Box 84, Lincoln, Christchurch, 7647, New Zealand
| | - Richard W McDowell
- Faculty of Agriculture and Life Sciences, Lincoln Univ., P.O. Box 84, Lincoln, Christchurch, 7647, New Zealand
- AgResearch, Lincoln Science Centre, Private Bag 4749, Christchurch, 8140, New Zealand
| | - Leo M Condron
- Faculty of Agriculture and Life Sciences, Lincoln Univ., P.O. Box 84, Lincoln, Christchurch, 7647, New Zealand
| | | | - Helen P Jarvie
- Dep. of Geography and Environmental Management, Univ. of Waterloo, Waterloo, ON, N2L 3G1, Canada
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16
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Zhang Q, Webber JS, Moyer DL, Chanat JG. An approach for decomposing river water-quality trends into different flow classes. THE SCIENCE OF THE TOTAL ENVIRONMENT 2021; 755:143562. [PMID: 33199002 DOI: 10.1016/j.scitotenv.2020.143562] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Revised: 10/29/2020] [Accepted: 11/03/2020] [Indexed: 06/11/2023]
Abstract
A number of statistical approaches have been developed to quantify the overall trend in river water quality, but most approaches are not intended for reporting separate trends for different flow conditions. We propose an approach called FN2Q, which is an extension of the flow-normalization (FN) procedure of the well-established WRTDS ("Weighted Regressions on Time, Discharge, and Season") method. The FN2Q approach provides a daily time series of low-flow and high-flow FN flux estimates that represent the lower and upper half of daily riverflow observations that occurred on each calendar day across the period of record. These daily estimates can be summarized into any time period of interest (e.g., monthly, seasonal, or annual) for quantifying trends. The proposed approach is illustrated with an application to a record of total nitrogen concentration (632 samples) collected between 1985 and 2018 from the South Fork Shenandoah River at Front Royal, Virginia (USA). Results show that the overall FN flux of total nitrogen has declined in the period of 1985-2018, which is mainly attributable to FN flux decline in the low-flow class. Furthermore, the decline in the low-flow class was highly correlated with wastewater effluent loads, indicating that the upgrades of treatment technology at wastewater treatment facilities have likely led to water-quality improvement under low-flow conditions. The high-flow FN flux showed a spike around 2007, which was likely caused by increased delivery of particulate nitrogen associated with sediment transport. The case study demonstrates the utility of the FN2Q approach toward not only characterizing the changes in river water quality but also guiding the direction of additional analysis for capturing the underlying drivers. The FN2Q approach (and the published code) can easily be applied to widely available river monitoring records to quantify water-quality trends under different flow conditions to enhance understanding of river water-quality dynamics.
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Affiliation(s)
- Qian Zhang
- University of Maryland Center for Environmental Science, Chesapeake Bay Program Office, Annapolis, MD, USA.
| | - James S Webber
- U.S. Geological Survey, Virginia and West Virginia Water Science Center, Richmond, VA, USA
| | - Douglas L Moyer
- U.S. Geological Survey, Virginia and West Virginia Water Science Center, Richmond, VA, USA
| | - Jeffrey G Chanat
- U.S. Geological Survey, Virginia and West Virginia Water Science Center, Richmond, VA, USA
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17
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Zhang Q, Fisher TR, Trentacoste EM, Buchanan C, Gustafson AB, Karrh R, Murphy RR, Keisman J, Wu C, Tian R, Testa JM, Tango PJ. Nutrient limitation of phytoplankton in Chesapeake Bay: Development of an empirical approach for water-quality management. WATER RESEARCH 2021; 188:116407. [PMID: 33065415 DOI: 10.1016/j.watres.2020.116407] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2020] [Revised: 09/04/2020] [Accepted: 09/06/2020] [Indexed: 06/11/2023]
Abstract
Understanding the temporal and spatial roles of nutrient limitation on phytoplankton growth is necessary for developing successful management strategies. Chesapeake Bay has well-documented seasonal and spatial variations in nutrient limitation, but it remains unknown whether these patterns of nutrient limitation have changed in response to nutrient management efforts. We analyzed historical data from nutrient bioassay experiments (1992-2002) and data from long-term, fixed-site water-quality monitoring program (1990-2017) to develop empirical approaches for predicting nutrient limitation in the surface waters of the mainstem Bay. Results from classification and regression trees (CART) matched the seasonal and spatial patterns of bioassay-based nutrient limitation in the 1992-2002 period much better than two simpler, non-statistical approaches. An ensemble approach of three selected CART models satisfactorily reproduced the bioassay-based results (classification rate = 99%). This empirical approach can be used to characterize nutrient limitation from long-term water-quality monitoring data on much broader geographic and temporal scales than would be feasible using bioassays, providing a new tool for informing water-quality management. Results from our application of the approach to 21 tidal monitoring stations for the period of 2007-2017 showed modest changes in nutrient limitation patterns, with expanded areas of nitrogen-limitation and contracted areas of nutrient saturation (i.e., not limited by nitrogen or phosphorus). These changes imply that long-term reductions in nitrogen load have led to expanded areas with nutrient-limited phytoplankton growth in the Bay, reflecting long-term water-quality improvements in the context of nutrient enrichment. However, nutrient limitation patterns remain unchanged in the majority of the mainstem, suggesting that nutrient loads should be further reduced to achieve a less nutrient-saturated ecosystem.
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Affiliation(s)
- Qian Zhang
- University of Maryland Center for Environmental Science / Chesapeake Bay Program, 410 Severn Avenue, Annapolis, MD 21403, USA.
| | - Thomas R Fisher
- University of Maryland Center for Environmental Science, Horn Point Laboratory, 2020 Horns Point Rd, Cambridge, MD 21613, USA
| | - Emily M Trentacoste
- U.S. Environmental Protection Agency, Chesapeake Bay Program Office, 410 Severn Avenue, Annapolis, MD 21403, USA
| | - Claire Buchanan
- Interstate Commission on the Potomac River Basin, 30 West Gude Drive, Suite 450, Rockville, MD 20850, USA
| | - Anne B Gustafson
- University of Maryland Center for Environmental Science, Horn Point Laboratory, 2020 Horns Point Rd, Cambridge, MD 21613, USA
| | - Renee Karrh
- Maryland Department of Natural Resources, 580 Taylor Ave, Annapolis, MD 21401, USA
| | - Rebecca R Murphy
- University of Maryland Center for Environmental Science / Chesapeake Bay Program, 410 Severn Avenue, Annapolis, MD 21403, USA
| | - Jennifer Keisman
- U.S. Geological Survey, MD-DE-DC Water Science Center, 5522 Research Park Drive, Catonsville, MD 21228, USA
| | - Cuiyin Wu
- Chesapeake Research Consortium / Chesapeake Bay Program, 410 Severn Avenue, Annapolis, MD 21403, USA
| | - Richard Tian
- University of Maryland Center for Environmental Science / Chesapeake Bay Program, 410 Severn Avenue, Annapolis, MD 21403, USA
| | - Jeremy M Testa
- University of Maryland Center for Environmental Science, Chesapeake Biological Laboratory, 146 Williams Street, Solomons, MD 20688, USA
| | - Peter J Tango
- U.S. Geological Survey / Chesapeake Bay Program, 410 Severn Avenue, Annapolis, MD 21403, USA
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18
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Ator SW, Blomquist JD, Webber JS, Chanat JG. Factors driving nutrient trends in streams of the Chesapeake Bay watershed. JOURNAL OF ENVIRONMENTAL QUALITY 2020; 49:812-834. [PMID: 33016477 DOI: 10.1002/jeq2.20101] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Accepted: 05/11/2020] [Indexed: 05/23/2023]
Abstract
Despite decades of effort toward reducing nitrogen and phosphorus flux to Chesapeake Bay, water-quality and ecological responses in surface waters have been mixed. Recent research, however, provides useful insight into multiple factors complicating the understanding of nutrient trends in bay tributaries, which we review in this paper, as we approach a 2025 total maximum daily load (TMDL) management deadline. Improvements in water quality in many streams are attributable to management actions that reduced point sources and atmospheric nitrogen deposition and to changes in climate. Nutrient reductions expected from management actions, however, have not been fully realized in watershed streams. Nitrogen from urban nonpoint sources has declined, although water-quality responses to urbanization in individual streams vary depending on predevelopment land use. Evolving agriculture, the largest watershed source of nutrients, has likely contributed to local nutrient trends but has not affected substantial changes in flux to the bay. Changing average nitrogen yields from farmland underlain by carbonate rocks, however, may suggest future trends in other areas under similar management, climatic, or other influences, although drivers of these changes remain unclear. Regardless of upstream trends, phosphorus flux to the bay from its largest tributary has increased due to sediment infill in the Conowingo Reservoir. In general, recent research emphasizes the utility of input reductions over attempts to manage nutrient fate and transport at limiting nutrients in surface waters. Ongoing research opportunities include evaluating effects of climate change and conservation practices over time and space and developing tools to disentangle and evaluate multiple influences on regional water quality.
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Affiliation(s)
- Scott W Ator
- USGS, 5522 Research Park Dr., Baltimore, MD, 21228, USA
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Abstract
Streambank legacy sediments can contribute substantial amounts of sediments to Mid-Atlantic waterways. However, there is uncertainty about the sediment-bound P inputs and the fate of legacy sediment P in surface waters. We compared legacy sediment P concentrations against other streambank sediments and upland soils and evaluated a variety of P indices to determine if legacy sediments are a source or sink of P to surface waters. Legacy sediments were collected from 15 streambanks in the mid-Atlantic USA. Total P and M3P concentrations and % degree of phosphorus saturation (DPS) values for legacy sediments were lower than those for upland soils. % DPS values for legacy sediments were below the water quality threshold for P leaching. Phosphorus sorption index (PSI) values for legacy sediments indicated a large capacity for P sorption. On the other hand, equilibrium phosphorus concentration (EPC0) for legacy sediments suggested that they could be a source or a sink depending on stream water P concentrations. Anoxic conditions resulted in a greater release of P from legacy sediments compared to oxic conditions. These results suggest that legacy sediment P behavior could be highly variable and watershed models will need to account for this variability to reliably quantify the source-sink behavior of legacy sediments in surface waters.
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Li NX, Xu JF, Yin W, Chen QZ, Wang J, Shi ZH. Effect of local watershed landscapes on the nitrogen and phosphorus concentrations in the waterbodies of reservoir bays. THE SCIENCE OF THE TOTAL ENVIRONMENT 2020; 716:137132. [PMID: 32045768 DOI: 10.1016/j.scitotenv.2020.137132] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/14/2019] [Revised: 02/03/2020] [Accepted: 02/03/2020] [Indexed: 06/10/2023]
Abstract
Reservoir bays, which are affected by the reservoir and watershed characteristics, are the initial and most sensitive areas in the evolution process of reservoir water quality. However, the relationship between the watershed characteristics and nitrogen and phosphorus concentrations in reservoir bays is poorly understood. We selected 66 bays from the Danjiangkou Reservoir and sampled twice per year (storage and discharge periods) from 2015 to 2018 to monitor the total nitrogen (TN) and total phosphorus (TP) concentration in the waterbodies of the reservoir bays. Four types of watershed characteristic indices (topographic variables, soil variables, land-use composition, and landscape patterns) around these bays were obtained. We quantified the relationship between the TN and TP concentrations and watershed characteristics in the waterbodies of the reservoir bays using partial least squares regression (PLSR). The results showed that the mean concentrations of TN and TP in the storage period (TN:1.69 mg·L-1, TP:0.088 mg·L-1) were higher than those in the discharge period (TN:1.22 mg·L-1, TP:0.063 mg·L-1). The optimal PLSR models explained 67.9% and 82.5% of the TN concentration variability, and 65.4% and 67.2% of the TP concentration variability during the storage and discharge period, respectively. Based on the variable importance in the projection (VIP) values, soil erodibility had significant effects on the TN and TP concentrations. The key factors affecting the TN concentration were the slope gradient, basin relief, topographic wetness index, forest and agricultural land use, whereas the factors controlling the TP concentration were the landscape shape index, edge density, Shannon's diversity index and grass land use, although the TP concentration was also controlled by the patch density and contagion during the storage period, and by mean patch size and largest patch index during the discharge period. This study provides critical insights into sustainable landscape planning and effective reservoir water quality management.
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Affiliation(s)
- N X Li
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an 710061, China
| | - J F Xu
- The Yangtze River Water Resources Protection Science Institute, Wuhan 430051, China
| | - W Yin
- The Yangtze River Water Resources Protection Science Institute, Wuhan 430051, China
| | - Q Z Chen
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an 710061, China
| | - J Wang
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an 710061, China.
| | - Z H Shi
- College of Resources and Environment, Huazhong Agricultural University, Wuhan 430070, China; State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences, Yangling, Shaanxi 712100, China; CAS Center for Excellence in Quaternary Science and Global Change, Xi'an 710061, China.
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Kleinman PJA, Fanelli RM, Hirsch RM, Buda AR, Easton ZM, Wainger LA, Brosch C, Lowenfish M, Collick AS, Shirmohammadi A, Boomer K, Hubbart JA, Bryant RB, Shenk GW. Phosphorus and the Chesapeake Bay: Lingering Issues and Emerging Concerns for Agriculture. JOURNAL OF ENVIRONMENTAL QUALITY 2019; 48:1191-1203. [PMID: 31589735 DOI: 10.2134/jeq2019.03.0112] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Hennig Brandt's discovery of phosphorus (P) occurred during the early European colonization of the Chesapeake Bay region. Today, P, an essential nutrient on land and water alike, is one of the principal threats to the health of the bay. Despite widespread implementation of best management practices across the Chesapeake Bay watershed following the implementation in 2010 of a total maximum daily load (TMDL) to improve the health of the bay, P load reductions across the bay's 166,000-km watershed have been uneven, and dissolved P loads have increased in a number of the bay's tributaries. As the midpoint of the 15-yr TMDL process has now passed, some of the more stubborn sources of P must now be tackled. For nonpoint agricultural sources, strategies that not only address particulate P but also mitigate dissolved P losses are essential. Lingering concerns include legacy P stored in soils and reservoir sediments, mitigation of P in artificial drainage and stormwater from hotspots and converted farmland, manure management and animal heavy use areas, and critical source areas of P in agricultural landscapes. While opportunities exist to curtail transport of all forms of P, greater attention is required toward adapting P management to new hydrologic regimes and transport pathways imposed by climate change.
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Zhang C, Guo S, Zhang F, Engel BA, Guo P. Towards sustainable water resources planning and pollution control: Inexact joint-probabilistic double-sided stochastic chance-constrained programming model. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 657:73-86. [PMID: 30530221 DOI: 10.1016/j.scitotenv.2018.11.463] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 11/14/2018] [Accepted: 11/30/2018] [Indexed: 06/09/2023]
Abstract
This study presents an inexact joint-probabilistic double-sided stochastic chance-constrained programming (IJDSCCP) model for sustainable water resources planning and pollution control in water quality management systems under uncertainty. Techniques of interval parameter programming (IPP), joint-probabilistic programming (JPP) and double-sided stochastic chance-constrained programming (DSCCP) are incorporated into a modeling framework. The IJDSCCP can not only address uncertainties presented as interval parameters and double-sided randomness (i.e. both left-hand and right-hand sides) that are characterized as normal distributions, but also examine the reliability level of satisfying the entire system constraints. It further improves upon conventional stochastic chance-constrained programming for handing random uncertainties in the left-hand and right-hand sides of constraints. Moreover, a non-equivalent but sufficient linearization form of the IJDSCCP is presented to solve such a problem. Then, the model is applied to a representative case for water resources planning and pollution control. The results including water resources planning solutions, pollution control plans and system benefits under the combinations of different joint and individual probability levels will be obtained. The solutions are expressed as combinations of deterministic, interval and distributional information, which can facilitate analysis of different forms of uncertainties. After investigating and comparing the variations of results, it is found that an increasing joint probability level can lead to higher system benefits, i.e., [13,841.68, 21,801.81] × 106 Yuan (p = 0.01, p1 = 0.0033, p2 = 0.0033 and p3 = 0.0033), [14,150.26, 22,260.06] × 106 Yuan (p = 0.05, p1 = 0.0166, p2 = 0.0166 and p3 = 0.0166) and [14,280.55, 22,415.52] × 106 Yuan (p = 0.10, p1 = 0.033, p2 = 0.033 and p3 = 0.033). A set of decreased individual probability levels gives rise to the maximum system benefits at the same joint probability level. Furthermore, the results of the IJDSCCP are compared with a general interval-based optimization framework as well. Therefore, the results from the IJDSCCP are valuable for assisting managers in generating and identifying decision alternatives under different scenarios.
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Affiliation(s)
- Chenglong Zhang
- Center for Agricultural Water Research in China, College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
| | - Shanshan Guo
- Center for Agricultural Water Research in China, College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
| | - Fan Zhang
- Center for Agricultural Water Research in China, College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
| | - Bernard A Engel
- Department of Agricultural and Biological Engineering, Purdue University, West Lafayette, IN 47907, USA.
| | - Ping Guo
- Center for Agricultural Water Research in China, College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China.
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Oelsner GP, Stets EG. Recent trends in nutrient and sediment loading to coastal areas of the conterminous U.S.: Insights and global context. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 654:1225-1240. [PMID: 30841397 DOI: 10.1016/j.scitotenv.2018.10.437] [Citation(s) in RCA: 37] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/27/2018] [Revised: 10/29/2018] [Accepted: 10/31/2018] [Indexed: 05/16/2023]
Abstract
Coastal areas in the U.S. and worldwide have experienced massive population and land-use changes contributing to significant degradation of coastal ecosystems. Excess nutrient pollution causes coastal ecosystem degradation, and both regulatory and management efforts have targeted reducing nutrient and sediment loading to coastal rivers. Decadal trends in flow-normalized nutrient and sediment loads were determined for 95 monitoring locations on 88 U.S. coastal rivers, including tributaries of the Great Lakes, between 2002 and 2012 for nitrogen (N), phosphorus (P), and sediment. N and P loading from urban watersheds generally decreased between 2002 and 2012. In contrast, N and P trends in agricultural watersheds were variable indicating uneven progress in decreasing nutrient loading. Coherent decreases in N loading from agricultural watersheds occurred in the Lake Erie basin, but limited benefit is expected from these changes because P is the primary driver of degradation in the lake. Nutrient loading from undeveloped watersheds was low, but increased between 2002 and 2012, possibly indicating degradation of coastal watersheds that are minimally affected by human activities. Regional differences in trends were evident, with stable nutrient loads from the Mississippi River to the Gulf of Mexico, but commonly decreasing N loads and increasing P loads in Chesapeake Bay. Compared to global rivers, coastal rivers of the conterminous U.S have somewhat lower TN yields and slightly higher TP yields, but similarities exist among land use, nutrient sources, and changes in nutrient loads. Despite widespread decreases in N loading in coastal watersheds, recent N:P ratios remained elevated compared to historic values in many areas. Additional progress in reducing N and P loading to U.S. coastal waters, particularly outside of urban areas, would benefit coastal ecosystems.
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Affiliation(s)
- Gretchen P Oelsner
- U.S. Geological Survey, New Mexico Water Science Center, 6700 Edith Blvd. NE, Bldg. B, Albuquerque, NM 87111, USA.
| | - Edward G Stets
- U.S. Geological Survey, Earth System Processes Division, 3215 Marine Street, Ste. E-127, Boulder, CO 80303, USA.
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