Sediments in Agricultural Reservoirs Act as Sinks and Sources for Nutrients over Various Timescales

Abstract

Reservoirs along rivers have the potential to act as nutrient sinks (e.g., denitrification and sedimentation) or sources (e.g., decomposition and redox changes), potentially reducing or enhancing nutrient loads downstream. This study investigated the spatial and temporal variability of water and lakebed sediment chemistry for an agricultural reservoir, Carlyle Lake (Illinois, U.S.), to assess the role of sediments as nutrient sinks or sources. Samples were collected across the reservoir over a 2‐year period. We measured N‐ and P‐species in water at the sediment‐water interface, in sediment porewaters, and loosely bound to sediment exchange sites. Total N, total P, total C, organic matter, Fe, Mn, and grain size were measured in bulk sediments. We observed a strong gradient in sedimentary total N, total P, total C, organic matter, and metals along the reservoir, with the lowest concentrations at the river mouth and the highest concentrations near the dam. Additionally, we did a long‐term nutrient mass balance using historical water quality data for streams entering and exiting the reservoir and the reservoir itself. Mass balance calculations showed that Carlyle Lake, on average, removed 2,738 Mg N/year and released 121 Mg P/year over the multidecadal observation period. While N was consistently removed from the system over time, P was initially stored in, but later released from, the reservoir. The subsequent release of legacy P from the reservoir led to higher outgoing, compared with incoming, P loads. Thus, reservoirs in intensively managed landscapes can act as sinks for N but sources for P over decadal timescales.

Sediment Nutrient Flux Rates in a Shallow, Turbid Lake Are More Dependent on Water Quality Than Lake Depth

“…We also hypothesized that sediment NO 3 − uptake would be higher in deeper water, and SRP uptake would be higher in shallower water. This hypothesis was based on predictions from previous studies that O 2 availability would be lower in deeper water sediments where light and primary production is excluded, as low redox potential can increase NO 3 − loss through denitrification and increase SRP release from bound sediments [18,29,51]. We found no differences in sediment nutrient flux based on water depth, and similar flux rates were observed from shore to mid-lake.…”

“…The time of year and seasonality can have varying effects on nutrient fluxes. For example, Jin et al [31] observed seasonal changes in sediment P cycling, but Shaughnessey et al [18] did not observe seasonal influences on sediment N fluxes. The relationship between nutrient removal and temperature has long been established due to increased biologic activity at warmer temperatures, which, in turn, increases total nutrient retention, specifically through denitrification [65,66].…”

Structural and functional comparisons of the environmental microbiota of pond and tank environments at different locations for the commercial aquaculture of American shad

“…Custodio et al (2020) suggested that the bacterial communities in lake environments experienced stress from fish farming in the Peruvian Andes. Microorganisms usually sink into the sediment of aquaculture water and eventually become a source of nutrients for aquatic organisms (Shaughnessy et al 2019). Carbone and Faggio (2016) suggested that the microbiota played a vital role in defining the yield and quality of products from fisheries and other aquaculture environments.…”

Degree of Anthropogenic Land Disturbance Controls Fluvial Sediment Hysteresis

“…Sediment pollution of water bodies can result in aquatic habitat degradation, hindered water supply, and transport of pollutants; thus, it is of major concern to watershed managers. Effective sediment management necessitates insight into active sediment sources and pathways along with their response to hydroclimatic variables, geomorphological features, and land management operations.…”