Biogeochemical hotspots: Role of small water bodies in landscape nutrient processing

Abstract

Increased loading of nitrogen (N) and phosphorus (P) from agricultural and urban intensification has led to severe degradation of inland and coastal waters. Lakes, reservoirs, and wetlands (lentic systems) retain these nutrients, thus regulating their delivery to downstream waters. While the processes controlling N and P retention are relatively well-known, there is a lack of quantitative understanding of how these processes manifest across spatial scales. We synthesized data from 600 lentic systems around the world to gain insight into the relationship between hydrologic and biogeochemical controls on nutrient retention. Our results indicate that the first-order reaction rate constant, k [T 21 ], is inversely proportional to the hydraulic residence time, s [T], across 6 orders of magnitude in residence time for total N, total P, nitrate, and phosphate. We hypothesized that the consistency of the relationship points to a strong hydrologic control on biogeochemical processing, and validated our hypothesis using a sediment-water model that links major nutrient removal processes with system size. Finally, the k-s relationships were upscaled to the landscape scale using a wetland size-frequency distribution. Results suggest that small wetlands play a disproportionately large role in landscape-scale nutrient processing-50% of nitrogen removal occurs in wetlands smaller than 10 2.5 m 2 in our example. Thus, given the same loss in wetland area, the nutrient retention potential lost is greater when smaller wetlands are preferentially lost from the landscape. Our study highlights the need for a stronger focus on small lentic systems as major nutrient sinks in the landscape. Plain Language Summary Excess nutrient pollution from intensive fertilizer use and farming operations poses an increasing threat to water quality worldwide. Lakes, streams, and wetlands restrict the movement of nutrients, and thus protect downstream waters. We have a limited understanding, however, of how removal processes are affected by the size and type of the water body. Based on a synthesis of data from lakes, reservoirs, and wetlands worldwide, we found that smaller water bodies tend to have higher nutrient removal rates. We applied our findings to the landscape scale and found that for the same wetland area lost, the loss of small wetlands corresponds to a greater loss in wetland nutrient removal potential. Such findings are significant to wetland protection and restoration efforts, which have historically focused on maximizing total wetland area rather than on preserving a distribution of different wetlands sizes within a landscape.

Drivers of Sediment Accumulation and Nutrient Burial in Coastal Stormwater Detention Ponds, South Carolina, USA

“…Second, small waterbodies have been identified as hotspots of biogeochemical activity and environmental pollutant exposure, with sediments being a key site of C and nutrient reprocessing and burial (Stanley 1996;Wu and others 1996;Comings and others 2000;Mallin and others 2002;Downing 2010;Weinstein and others 2010;Cheng and Basu 2017). Indeed, there is growing interest in the role that inland waters, including so-called artificial water bodies, play in global C cycling (Cole and others 2007;Tranvik and others 2009).…”

“…Though there has been extensive research into the impacts of urbanization on the biogeochemical cycles of lotic systems others 2005,2012;Booth and others 2016), urban ponds have not received the same level of attention. There is still only a limited understanding of the role stormwater ponds play in urban biogeochemical cycles (Williams and others 2013;Chiandet and Xenopoulos 2016;Cheng and Basu 2017). This is especially true in coastal urban centers where stormwater runoff and pond discharges directly enter estuarine and marine receiving waters.…”

“…Historically, the study of limnology has been skewed toward larger lentic systems; only recently has the ecological significance of smaller water bodies been recognized (Downing 2010;Cheng and Basu 2017). Although the importance of small water bodies is gaining more attention, there is still a knowledge gap surrounding the response of small lentic systems to urban and suburban development.…”

Modeling Connectivity of Non‐floodplain Wetlands: Insights, Approaches, and Recommendations

“…), chemical (e.g., Marton et al. ; Cheng and Basu ), and biological (e.g., Fairbairn and Dinsmore ; Zamberletti et al. ) services; yet, these systems are being lost at increasing rates (VanMeter and Basu ; Serran and Creed ; Sofaer et al.…”

“…NFW connectivity varies over time and space (Evenson et al. ), and when considered at watershed scale, NFW connectivity can influence watershed hydrology and downstream flows, with associated influences on biogeochemical (e.g., Cheng and Basu ) and biological (e.g., Zamberletti et al. ) function and condition.…”