Quantifying flow-ecology relationships across flow regime class and ecoregions in South Carolina

Fish beta diversity associated with hydrologic and anthropogenic disturbance gradients in contrasting stream flow regimes

Understanding the role of hydrologic variation in structuring aquatic communities is crucial for successful conservation and sustainable management of native freshwater biodiversity. Partitioning beta diversity into the additive components of spatial turnover and nestedness can provide insight into the forces driving variability in fish assemblages across stream flow regimes. We examined stream fish beta diversity across hydrologic and anthropogenic disturbance gradients using long-term (1916-2016) site occurrence records (n = 17,375) encompassing 252 species. We assessed total beta diversity (Sørensen dissimilarity), spatial turnover, and nestedness of fish assemblages in contrasting stream flow regimes across a gradient of decreasing flow stability: groundwater stable (n = 77), groundwater (n = 67), groundwater flashy (n = 175), perennial runoff (n = 141), runoff flashy (n = 255), and intermittent (n = 63) streams. Differences in total beta diversity among the stream flow regimes were driven predominantly (>86 %) by spatial turnover (i.e. species replacement) as opposed to nestedness (i.e. species loss or gain). Total fish beta diversity and spatial turnover were highest in streams with intermediate flow stability (groundwater flashy), while more flow-stable streams (groundwater stable and groundwater) had lower turnover and higher nestedness. Species turnover was also strongly associated with seasonal variation in hydrology across all flow regimes, but these relationships were most evident for assemblages in intermittent streams. Distance-based statistical comparisons showed significant correlations between beta diversity and anthropogenic disturbance variables, including dam density, dam storage volume and water withdrawals in catchments of groundwater stable streams, while hydrologic variables were more strongly correlated with beta diversity in streams with runoff-dominated and flashy flow regimes. The high spatial turnover of species implies that fish conservation actions would benefit from watershed-focused approaches targeting multiple streams with wide spatial distribution, as opposed to simply focusing on preserving sites with the greatest number of species.

Linking wastewater treatment plant effluents to water quality and hydrology: Effects of multiple stressors on fish communities

Wastewater treatment plants (WWTPs) are essential for maintaining a good water quality of surface waters. However, WWTPs are also associated with water quality deterioration and hydro-morphological alteration. Riverine communities respond to these stressors with changes in their community structure, abundance and diversity. In this study, we used a dataset of 94 monitoring sites across North Rhine-Westphalia, Germany to investigate the influence of WWTPs on the water quality and hydro-morphological quality in river sections downstream of WWTP effluents. More specifically, we analyzed the effects of the percentage of WWTP effluents (in relation to median base flow) on four stressor groups (physico-chemistry, micropollutants, hydrological and morphological alteration) using Linear Mixed Models (LMM). Furthermore, we assessed the impact of a selection of twelve ecologically relevant stressor variables reflecting water quality deterioration and hydro-morphological alteration on reference fish communities using Canonical Correspondence Analysis (CCA). The percentage of WWTP effluents was correlated with water quality, especially with toxic units of a wide range of pharmaceuticals including diclofenac, venlafaxine and sulfamethoxazole (R² up to 0.54) as well as specific pesticides (e.g., terbutryn: R² = 0.33). The correlation of percent WWTP effluents with hydro-morphological alteration was weaker and most pronounced for the frequency of high flow (R² = 0.24) and flow variability (R² = 0.19). About 40 % of the variance in the fish community structure were explained by 12 stressor variables in the CCA models. Water quality and hydrological, but not morphological stressors showed strong albeit highly variable effects on individual fish species. The results indicate that water quality degradation and hydrological alteration are important factors determining the ecological status of fish communities. In this context, WWTP effluents can impose relevant point sources of pollution that affect water quality but also cause alterations of the hydrological regime. Further management measures addressing both stressor groups are needed to improve the ecological status.

Integrating fish swimming abilities into rapid road crossing barrier assessment: Case studies in the southeastern United States

Many aquatic networks are fragmented by road crossing structures; remediating these barriers to allow fish passage is critical to restoring connectivity. Maximizing connectivity requires effective barrier identification and prioritization, but many barrier prioritization efforts do not consider swimming capabilities of target species. Given the many potential barriers within watersheds, inventory efforts integrating species-specific swimming speeds into rapid assessment protocols may allow for more accurate barrier removal prioritization. In this study, we demonstrate an approach for integrating fish swimming speeds into rapid barrier assessment and illustrate its utility via two case studies. We measured critical swimming speeds (Ucrit) of two stream-resident fish species with very different swimming modes: Yoknapatawpha Darter (Etheostoma faulkneri), an at-risk species whose current distribution is restricted to highly degraded habitat, and Bluehead Chub (Nocomis leptocephalus), an important host species for the federally endangered Carolina Heelsplitter mussel (Lasmigona decorata). We assessed potential barriers for Yoknapatawpha Darters in the Mississippi-Yocona River watershed, and Bluehead Chubs in the Stevens Creek watershed, South Carolina, USA. We integrated Ucrit into the Southeast Aquatic Resources Partnership (SARP) barrier assessment protocol by estimating the proportion of individuals per species swimming at least as fast as the current through the assessed structures. Integrating Ucrit estimates into the SARP protocol considerably increased barrier severity estimates and rankings only for Yoknapatawpha Darters in the Yocona River watershed. These results indicate the importance of including species-specific swimming abilities in rapid barrier assessments and the importance of species-watershed contexts in estimating where swimming speed information might be most important. Our method has broad application for those working to identify barriers more realistically to improve species-specific fish passage. This work represents a next step in improving rapid barrier assessments and could be improved by investigating how results change with different measurements of swimming abilities and structure characteristics.

The value of improving freshwater ecosystem services: South Carolina residents' willingness to pay for improved water quality

Riverine ecosystems play a crucial role in providing essential services such as drinking water, food, recreation, and other aquatic resources. Yet, their capacity to deliver ecosystem services is threatened by rapid land use which modifies their ecological functions. While freshwater monitoring and restoration programs became more robust with technological advancement, the technical ecosystem indicators monitored by experts do not typically resonate with the public. Since public sentiments and preferences are crucial in conservation planning, we quantified households' mean willingness to pay (WTP) for riverine ecosystem services in South Carolina (SC) using a payment card approach. This technique in conducting a contingent valuation method allowed us to estimate mean WTP for five aquatic indicators. Findings revealed that households' monthly mean WTP is higher for indicators that can enhance recreational benefits, such as fish catch ($5.89- $6.58), species richness ($6.28- $6.72) and access ($6.75) compared to IBI ($5.74- $6.26) and instream flow quality ($5.34-6.06). When extrapolated to entire SC, the improvement of each indicator would translate to total benefits ranging between $131 to $165 million annually. The values computed from this study could serve as inputs for the computation of benefit-cost ratios of proposed freshwater programs. By incorporating households' WTP in the policy analysis, decision makers can prioritize programs that offer the greatest public benefit, while enhancing freshwater quality across the state.

Assessing the added value of antecedent streamflow alteration information in modeling stream biological condition

In stream systems, disentangling relationships between biology and flow and subsequent prediction of these relationships to unsampled streams is a common objective of large-scale ecological modeling. Often, streamflow metrics are derived from aggregating continuous streamflow records available at a subset of stream gages into long-term flow regime descriptors. Despite demonstrated value, shortcomings of these long-term approaches include spatial restriction to locations with long-term continuous flow records (commonly, biased toward larger systems) and omission of potentially ecologically important short-term (i.e., ≤1 year) antecedent streamflow information. We used long-term flow regime and short-term antecedent streamflow alteration information to evaluate relative performance in modeling stream fish biological condition. We compared results to understand whether short-term antecedent streamflow information improved models of fish biological condition. Results indicated that models incorporating short-term antecedent data performed better than those relying solely on long-term flow regime data (kappa statistic = 0.29 and 0.23, respectively) and improved prediction accuracy among stream sizes and in six of nine ecoregions. Additionally, models relying solely on short-term streamflow information performed similarly to those with only long-term streamflow information (kappa = 0.23). Incorporating short-term antecedent streamflow metrics may provide added ecological information not fully captured by long-term flow regime summaries in macroscale modeling efforts or perform similarly to long-term streamflow data when long-term data are not available.

Identification and restoration of hydrological processes alteration during the fish spawning period

The hydrological processes play an important role in stimulating fish spawning behavior. Changes in the natural hydrological processes will alter the populations and distribution of fish, which may have a negative impact on the native aquatic organisms. The aim of this study is to identify the alteration of the water rising process during the fish spawning period and to construct an ecological flow optimization model to restore the water rising conditions for fish reproduction. The Mann-Kendall test and the sliding t-test were used to detect the mutation year of the mean daily flow data sets in the fish spawning period in each monitoring year. Then the data sets can be divided into pre-altered and post-altered periods. The water rising process was characterized by the water rising processes count, the duration, the daily flow increase rate, the date of the water rising process, and the initial water rising flow. The changes in hydrological processes in the middle reaches of the Yangtze River were investigated by comparing the post-altered and pre-altered characteristic parameters. Furthermore, we integrated the statistical values of the five characteristic parameters in pre-altered into an ecological flow optimization model to simulate the natural water rising processes for the spawning of the Four Major Chinese Carps (FMCC) and Chinese Sturgeon (CS). The analysis showed that after the hydrological mutation year, the duration and the initial water rising flow in the FMCC spawning season were increased, with hydrological alteration degrees of 63.10% and 70.16%, respectively; however, the daily flow increase rate was significantly decreased, with hydrological alteration of 86.50%. During the CS spawning season, the water rising processes count and the initial water rising flow were dramatically altered parameters, with hydrological alteration degrees of 50.86% and 83.27%, respectively. The former parameter increased, but the latter decreased significantly in the post-altered period. To induce the spawning activity of FMCC and CS, appropriate ecological flows and hydrological parameters were proposed. These results showed that during the spawning seasons of FMCC and CS, the hydrological processes of the middle reaches of the Yangtze River changed significantly. Therefore, ecological flow must be ensured through ecological operation of upstream reservoirs to provide suitable spawning conditions in target fish spawning grounds.

The effect of seasonality in predicting the level of crime. A spatial perspective

This paper presents an innovative methodology to study the application of seasonality (the existence of cyclical patterns) to help predict the level of crime. This methodology combines the simplicity of entropy-based metrics that describe temporal patterns of a phenomenon, on the one hand, and the predictive power of machine learning on the other. First, the classical Colwell's metrics Predictability and Contingency are used to measure different aspects of seasonality in a geographical unit. Second, if those metrics turn out to be significantly different from zero, supervised machine learning classification algorithms are built, validated and compared, to predict the level of crime based on the time unit. The methodology is applied to a case study in Barcelona (Spain), with month as the unit of time, and municipal district as the geographical unit, the city being divided into 10 of them, from a set of property crime data covering the period 2010-2018. The results show that (a) Colwell's metrics are significantly different from zero in all municipal districts, (b) the month of the year is a good predictor of the level of crime, and (c) Naive Bayes is the most competitive classifier, among those who have been tested. The districts can be ordered using the Naive Bayes, based on the strength of the month as a predictor for each of them. Surprisingly, this order coincides with that obtained using Contingency. This fact is very revealing, given the apparent disconnection between entropy-based metrics and machine learning classifiers.

Effects of environment and metacommunity delineation on multiple dimensions of stream fish beta diversity

Introduction

Beta diversity represents changes in community composition among locations across a landscape. While the effects of human activities on beta diversity are becoming clearer, few studies have considered human effects on the three dimensions of beta diversity: taxonomic, functional, and phylogenetic. Including anthropogenic factors and multiple dimensions of biodiversity may explain additional variation in stream fish beta diversity, providing new insight into how metacommunities are structured within different spatial delineations.

Methods

In this study, we used a 350 site stream fish abundance dataset from South Carolina, United States to quantify beta diversity explainable by spatial, natural environmental, and anthropogenic variables. We investigated three spatial delineations: (1) a single whole-state metacommunity delineated by political boundaries, (2) two metacommunities delineated by a natural geomorphic break separating uplands from lowlands, and (3) four metacommunities delineated by natural watershed boundaries. Within each metacommunity we calculated taxonomic, functional, and phylogenetic beta diversity and used variation partitioning to quantify spatial, natural environmental, and anthropogenic contributions to variations in beta diversity.

Results

We explained 25–81% of the variation in stream fish beta diversity. The importance of these three factors in structuring metacommunities differed among the diversity dimensions, providing complementary perspectives on the processes shaping beta diversity in fish communities. The effect of spatial, natural environmental, and anthropogenic factors varied among the spatial delineations, which indicate conclusions drawn from variation partitioning may depend on the spatial delineation chosen by researchers.

Discussion

Our study highlights the importance of considering human effects on metacommunity structure, quantifying multiple dimensions of beta diversity, and careful consideration of user-defined metacommunity boundaries in beta diversity analyses.

Establishment of watershed ecological water requirements framework: A case study of the Lower Yellow River, China

It is of great practical significance to ensure ecological water requirements (EWRs) for the maintenance of river health and the sustainable development of human socioeconomics. How to scientifically determine the comprehensive EWRs and estimate the uncertainty of hydro-ecological tools performed in the process of conducting remains one of the most important yet most complicated issues. In this study, the ecological water requirements framework (EWRsF) of the Lower Yellow River (LYR), which considers instream ecological base flow, survival and reproduction of indicator fish species, equilibrium of erosion and siltation and ecological function of the estuary, was constructed by integrating hydrological, hydraulic and ecological habitat methods. The framework contains three crucial components - determination of instream EWRs and estuarine EWRs, uncertainty analysis of hydro-ecological tools. For instream ecological base flow, we proposed an improved Tennant method, which took into account both seasonality and sediment transport characteristics of the LYR, and could better reflect the actual hydrological regime. For the hydrological ecological response relationship of indicator fish species, we estimated the uncertainty of the model output of River2D to improve its credibility of the simulation results. The results demonstrated that: 1) Two-grade intra-annual monthly EWRs process of suitable and minimum for four instream sections and estuary area were obtained. The flood season (June-October) is the period with the largest proportion of intra-annual instream EWRs, whereas in estuary area, is the spawning period (April-July) of dominant species. 2) The uncertainty of HSI curves directly leads to the uncertainty of model output. Although the shape and position of the WUA curve can be uncertain, it does not affect the judgment of EWRs threshold. 3) The research results can provide scientific basis for water resource management decision-making in the LYR. Additionally, the ideas also have reference significance for similar basins.