The 20th century whole-basin trophic history of an inter-drumlin lake in an agricultural catchment

Evaluation of real-time nutrient analysis of fertilized raspberry using petiole sap

The time delay in receiving conventional tissue nutrient analysis results caused red raspberry (Rubus idaeus L.) growers to be interested in rapid sap tests to provide real-time results to guide immediate nutrient management practices. However, sap analysis has never been conducted in raspberry. The present work aimed to evaluate the relationship of petiole sap nitrate (NO₃ ^-), potassium (K⁺), and calcium (Ca²⁺) concentrations measured using compact ion meters and leaf tissue total nitrogen (TN), potassium (K), and calcium (Ca) concentrations measured using conventional tissue nutrient analysis. The relationship of petiole sap NO₃ ^- and leaf tissue TN concentrations with plant growth and production variables was also explored. Fertilizer treatments of urea were surface applied to raised beds of established "Meeker" floricane red raspberry plots at control, low, medium, and high rates (0, 34, 67, and 101 kg N ha^-1, respectively) in 2019 and 2020. The experiment was arranged in a randomized complete block design with three replications. Whole leaves were collected from representative primocanes in mid- and late- July and August 2019 and 2020 (i.e., four sampling time points per year). At each sampling time point, a subsample of leaves was used for petiole sap analyses of NO₃ ^-, K⁺, and Ca²⁺ concentrations using compact ion meters, and conventional tissue testing of leaf tissue TN, K, and Ca concentrations, respectively. There were no interactions between N fertilizer rate and year nor between N fertilizer rate and sampling time. No significant differences were found due to N fertilizer rate for petiole sap NO₃ ^-, K⁺, Ca²⁺ nor leaf tissue TN, K, Ca concentrations. However, significant year and sampling time effects occurred in measured petiole sap and leaf tissue nutrient concentrations. Overall, the correlations between petiole sap NO₃ ^- and leaf tissue TN, petiole sap Ca²⁺ and leaf tissue Ca, petiole sap K⁺ and leaf tissue K concentrations were non-strong and inconsistent. Future research is warranted as the interpretation of correlations between raspberry petiole sap and leaf tissue nutrient concentrations were inconclusive.

Limited Impacts of Cover Cropping on Soil N-Cycling Microbial Communities of Long-Term Corn Monocultures

Cover cropping (CC) is a promising in-field practice to mitigate soil health degradation and nitrogen (N) losses from excessive N fertilization. Soil N-cycling microbial communities are the fundamental drivers of these processes, but how they respond to CC under field conditions is poorly documented for typical agricultural systems. Our objective was to investigate this relationship for a long-term (36 years) corn [Zea mays L.] monocultures under three N fertilizer rates (N0, N202, and N269; kg N/ha), where a mixture of cereal rye [Secale cereale L.] and hairy vetch [Vicia villosa Roth.] was introduced for two consecutive years, using winter fallows as controls (BF). A 3 × 2 split-plot arrangement of N rates and CC treatments in a randomized complete block design with three replications was deployed. Soil chemical and physical properties and potential nitrification (PNR) and denitrification (PDR) rates were measured along with functional genes, including nifH, archaeal and bacterial amoA, nirK, nirS, and nosZ-I, sequenced in Illumina MiSeq system and quantified in high-throughput quantitative polymerase chain reaction (qPCR). The abundances of nifH, archaeal amoA, and nirS decreased with N fertilization (by 7.9, 4.8, and 38.9 times, respectively), and correlated positively with soil pH. Bacterial amoA increased by 2.4 times with CC within N269 and correlated positively with soil nitrate. CC increased the abundance of nirK by 1.5 times when fertilized. For both bacterial amoA and nirK, N202 and N269 did not differ from N0 within BF. Treatments had no significant effects on nosZ-I. The reported changes did not translate into differences in functionality as PNR and PDR did not respond to treatments. These results suggested that N fertilization disrupts the soil N-cycling communities of this system primarily through soil acidification and high nutrient availability. Two years of CC may not be enough to change the N-cycling communities that adapted to decades of disruption from N fertilization in corn monoculture. This is valuable primary information to understand the potentials and limitations of CC when introduced into long-term agricultural systems.

A Comprehensive Network Integrating Signature Microbes and Crucial Soil Properties During Early Biological Soil Crust Formation on Tropical Reef Islands

Biological soil crusts (BSCs/biocrusts), which are distributed across various climatic zones and well-studied in terrestrial drylands, harbor polyextremotolerant microbial topsoil communities and provide ecological service for local and global ecosystem. Here, we evaluated BSCs in the tropical reef islands of the South China Sea. Specifically, we collected 41 BSCs, subsurface, and bare soil samples from the Xisha and Nansha Archipelagos. High-throughput amplicon sequencing was performed to analyze the bacterial, fungal, and archaeal compositions of these samples. Physicochemical measurement and enzyme activity assays were conducted to characterize the soil properties. Advanced computational analysis revealed 47 biocrust-specific microbes and 10 biocrust-specific soil properties, as well as their correlations in BSC microbial community. We highlighted the previously underestimated impact of manganese on fungal community regulation and BSC formation. We provide comprehensive insight into BSC formation networks on tropical reef islands and established a foundation for BSC-directed environmental restoration.

Modelling spatial and temporal variations of annual suspended sediment yields from small agricultural catchments

Estimates of sediment yield are important for ecological and geomorphological assessment of fluvial systems and for assessment of soil erosion within a catchment. Many regulatory frameworks, such as the Convention for the Protection of the Marine Environment of the North-East Atlantic, derived from the Oslo and Paris Commissions (OSPAR) require reporting of annual sediment fluxes. While they may be measured in large rivers, sediment flux is rarely measured in smaller rivers. Measurements of sediment transport at a national scale can be also challenging and therefore, sediment yield models are often utilised by water resource managers for the predictions of sediment yields in the ungauged catchments. Regression based models, calibrated to field measurements, can offer an advantage over complex and computational models due to their simplicity, easy access to input data and due to the additional insights into factors controlling sediment export in the study sites. While traditionally calibrated to long-term average values of sediment yields such predictions cannot represent temporal variations. This study addresses this issue in a novel way by taking account of the variation from year to year in hydrological variables in the developed models (using annual mean runoff, annual mean flow, flows exceeded in five percentage of the time (Q5) and seasonal rainfall estimated separately for each year of observations). Other parameters included in the models represent spatial differences influenced by factors such as soil properties (% poorly drained soils and % peaty soils), land-use (% pasture or % arable lands), channel slope (S1085) and drainage network properties (drainage density). Catchment descriptors together with year-specific hydrological variables can explain both spatial differences and inter-annual variability of suspended sediment yields. The methodology is demonstrated by deriving equations from Irish data-sets (compiled in this study) with the best model efficiency of 0.84 and best model fit of adjusted R² of 0.82. Presented approach shows the potential for regression based models to model contemporary suspended sediment yields in small river systems.

Variations in Bacterial Community in a Temperate Lake Associated with an Agricultural Watershed

Terrestrially derived carbon and nutrients are washed into lakes, providing nutritional drivers for both microbial heterotrophy and phototrophy. Changes in the quantity and diversity of carbon and nutrients exported from watersheds in response to alterations in long-term land use have led to a need for evaluation of the linkage between watershed-exported carbon and nutrients and bacterial community structure in watershed associated lakes. To learn more about these interactions, we investigated Muskrat Lake in Michigan, which has a well-defined moderately sized watershed dominated by agriculture. We measured the water chemistry, characterized the dissolved organic carbon, and determined the structure of the bacterial communities at the inlet and center of this lake (five depths per site) over the summer and fall of 2008. The lake had temporal and rain event-based fluctuations in water chemistry, as well as temporal and rain event-dependent shifts in bacterial communities as measured by terminal restriction fragment length polymorphism. Agricultural watershed inputs were observed in the lake during and after rain events. Terminal restriction fragment length polymorphism and 454 pyrosequencing of the bacterial communities indicated that there were differences over time and that the dominant phylotypes shifted between summer and late fall. Some populations (e.g., Polynucleobacter and Mycobacterium) increased during fall, while others (e.g., Gemmatimonas) diminished. Redundancy and partitioning analyses showed that water chemistry is highly correlated with variations in the bacterial community of the lake, which explained 34 % of the variations in the bacterial community. Dissolved organic carbon had the greatest effects on variations in the Muskrat Lake bacterial community (2 %). The results of this study provide information that will enable a better understanding of the interaction between the bacterial community of lakes and changes in chemical properties as a result of nutrient importation from the surrounding watershed.

A palaeolimnological investigation into nutrient impact and recovery in an agricultural catchment

Widespread deterioration in water quality as a result of anthropogenic activity has led to the development and implementation of measures aimed at the protection of water resources in the EU. To date, however, relatively little attention has been paid to the effectiveness of these measures. Evidence from an enrichment-sensitive lake permitted reconstructions of changes in ecological and chemical water quality over the last c. 150-200 years, a period that includes a mid to late 20th century intensification of agriculture that was widely experienced across the European Union and the subsequent implementation of measures aimed at protecting water resources against pollution from farming. The data show the development of a more nutrient-tolerant diatom community from early in the 20th century, while the main trophic changes occurred from the 1950s, with the site becoming eutrophic by the 1960s. Heightened enrichment is thought to be linked to enhanced levels of phosphorus (P) transfers from the surrounding grassland catchment owing to an intensification of agricultural activities locally. Most recently, since the late 1990s and particularly post-2007, evidence suggests a decrease in aquatic enrichment, despite continued increases in agricultural intensification. This decoupling is likely to mark a successful implementation in 2006 of measures aimed at decreasing diffuse nutrient transfers from catchments linked to agri-environmental policies in Europe. The research highlights the importance of enrichment-sensitive water bodies as sentinel sites in the monitoring of both external and internal nutrient loadings as agricultural activities and other pressures change within the context of implementing regulatory responses to earlier declines in water quality.

Lake sedimentary evidence of phosphorus, iron and manganese mobilisation from intensively fertilised soils

A study of historical P inputs to Friary Lough, Co. Tyrone, Northern Ireland used a multi-sediment core approach. One of the sediment cores taken from the littoral zone at 2.5m water depth showed exceptionally high P, Fe and Mn concentrations below 20 cm sediment depth. Concentrations increased to 14 mg Pg(-1), 238 mg Feg(-1) and 35 mg Mng(-1) in the sediment profile and compared with deep basin maxima of 7 mg Pg(-1), 70 mg Feg(-1) and 2 mg Mng(-1) in surface sediments at 8.5m water depth. It is proposed that the high concentrations in the littoral zone core are due to post-depositional intrusion of chemical-rich local groundwater from soils in adjacent fields that are excessively fertilised with organic slurry. Soil analyses showed Olsen-P concentrations in these fields up to 125 mgkg(-1) at the soil surface (0-7.5 cm) and 39 mgkg(-1) in the sub-soil at 20 cm depth. We suggest that the mobilisation of P, Fe and Mn is due to leaching following P saturation and/or the loss of P absorbing chemicals due to prolonged reduction and complexing in wet soils. Further work will explore this relationship and the nature of the hydrological pathways through soil.