Hydrologic Controls on Nitrogen Cycling Processes and Functional Gene Abundance in Sediments of a Groundwater Flow-Through Lake

Abstract

The fate and transport of inorganic nitrogen (N) is a critically important issue for human and aquatic ecosystem health because discharging N-contaminated groundwater can foul drinking water and cause algal blooms. Factors controlling N-processing were examined in sediments at three sites with contrasting hydrologic regimes at a lake on Cape Cod, MA. These factors included water chemistry, seepage rates and direction of groundwater flow, and the abundance and potential rates of activity of N-cycling microbial communities. Genes coding for denitrification, anaerobic ammonium oxidation (anammox), and nitrification were identified at all sites regardless of flow direction or groundwater dissolved oxygen concentrations. Flow direction was, however, a controlling factor in the potential for N-attenuation via denitrification in the sediments. Potential rates of denitrification varied from 6 to 4500 pmol N/g/h from the inflow to the outflow side of the lake, owing to fundamental differences in the supply of labile organic matter. The results of laboratory incubations suggested that when anoxia and limiting labile organic matter prevailed, the potential existed for concomitant anammox and denitrification. Where oxic lake water was downwelling, potential rates of nitrification at shallow depths were substantial (1640 pmol N/g/h). Rates of anammox, denitrification, and nitrification may be linked to rates of organic N-mineralization, serving to increase N-mobility and transport downgradient.

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

“…These dynamics are difficult to capture in a generalized modelling framework yet they can modify the nutrient dynamics of the system. For example, groundwater often has a different oxygen concentration than that of the sediment bed (may depend on if the groundwater is sourced from deep or shallow aquifer, and if the discharge is near the edge or bottom of the water body) and will alter the redox gradient and modify the denitrification rates in the system [Stoliker et al, 2016]. Similarly, the oxic level of the sediments determine the sourcesink dynamics of sorbed P. In oxic conditions, iron hydroxides are strongly bonded and limit the diffusive flux between the water-sediment interface; in anoxic conditions, the phosphorus is released [Van Cappellen and Berner, 1988;Slomp et al, 1996Slomp et al, , 1998].…”

Seasonal and Spatial Variation in the Location and Reactivity of a Nitrate‐Contaminated Groundwater Discharge Zone in a Lakebed

“…The water table aquifer connected hydraulically to Ashumet Pond was contaminated by disposal of treated wastewater onto surface infiltration beds for >60 years (LeBlanc, ; Repert et al, ). A portion of the wastewater contaminant plume discharges into Ashumet Pond in the vicinity of Fishermans Cove (McCobb et al, ; Stoliker et al, ), which is about 2‐years groundwater travel time downgradient from the infiltration bed location. The lake and the study site location are typical of settings where wastewater plumes from septic systems discharge to surface water environments.…”

“…The well‐characterized, groundwater contaminant plume at the Cape Cod site is more than 7 km long, 1.2 km wide, and 30 m thick and contains vertical gradients of biogeochemically reactive dissolved constituents, including O 2 , NO 3 − , NH 4 + , phosphate (PO 4 −3 ), Fe +2 , manganese (Mn +2 ), dissolved organic carbon (DOC), and dissolved salts (Barbaro et al, ; Böhlke et al, ; LeBlanc, ; McCobb et al, ; Repert et al, ; Smith, Howes, et al, ; Stoliker et al, ). The plume is in a sand and gravel water table aquifer whose physical and hydrologic characteristics have been described previously (Barber et al, ; Hess et al, ; Kent & Fox, ; LeBlanc et al, ).…”

Investigating the spatio‐temporal variations of nitrate leaching on a tea garden hillslope by combining HYDRUS‐3D and DNDC models

“…Soil hydrology affects the ‐N leaching by two ways. From the biochemical perspective, soil water reduces the soil air‐filled pore space, thus altering the redox reaction of soil N, and thereby changing the soil ‐N content that is available for leaching ( Castellano et al, ; Stoliker et al, ; Mekala and Nambi , ; Wu et al, ). From the physical perspective, soil water movement is an important driving force of the ‐N leaching ( Donner et al., ; Li et al, ).…”