Nutrient Cycling in an Agricultural Watershed: I. Phreatic Movement

Abstract

Much of the runoff from agricultural fields in the southeastern Coastal Plain is carried to a stream channel system in a shallow phreatic aquifer. This subsurface runoff often passes through a band of riparian forest before becoming streamflow. It is hypothesized that the riparian ecosystem acts as a nutrient sink and reduces the concentrations and loads of nutrients in the shallow aquifer before the nutrients reach the stream channel. Concentrations and loads (kg/m2) of NO3‐N, NH4‐N, organic N, dissolved molybdate‐reactive P1 total P, Ca, Mg, K, Cl, and SO4‐S were measured in shallow phreatic wells at 37 locations on an agricultural watershed near Tifton, Ga. Total water volume moving off the watershed in subsurface flow was < 1% of streamflow with corresponding small amounts of nutrients. Nitrate‐N, Ca, and Mg had significantly higher concentrations in field wells than in forest or streamside wells. Concentrations of Cl were not reduced as water moved from field to forest. Processes within the riparian zone apparently converted primarily inorganic N from fields (76% NO3‐N, 6% NH4‐N, 18% organic N) into primarily organic N in streamside wells (10% NO3‐N, 14% NH4‐N, and 76% organic N). Concentration differences between field and forest wells indicated the riparian forest's ability to act as a sink for NO3‐N, Ca, Mg, K, and SO4‐S. Due to their role as nutrient sinks, riparian forests are important in maintaining stream water quality on agricultural watersheds.

Riparian Corridors: A New Conceptual Framework for Assessing Nitrogen Buffering Across Biomes

“…For instance, nutrient spiraling theory postulated that the interaction of stream water with adjacent riparian ecosystems can result in major changes in nutrient cycling and retention ( Figure 1C, Minshall et al, 1983;Naiman and Décamps, 1990;Fisher et al, 1998). Since the 1980s, it has been known that riparian ecosystems have a large capacity to retain and remove nitrogen originating from upslope, highlighting their potential to regulate the exchange of material between terrestrial and aquatic ecosystems (Lowrance et al, 1984;Peterjohn and Correll, 1984;Jacobs and Gilliam, 1985;Burt et al, 2010 for a review). The bidirectional nature of the lateral exchange of material (from the catchment to the stream and vice versa) and their unique ecological and functional characteristics make riparian corridors quintessential ecotones (Naiman and Décamps, 1990).…”

Concentration and chemical species of iron in soils from groundwater/surface water ecotones

“…Several studies have reported on the retention of N0 3 by denitrification and plant uptake in the discharge zone (Lowrance et al, 1984;Lowrance, 1992, Haycock & Pinay, 1993 by comparing concentrations in groundwater and surface water. Lowrance et al (1983) also found a retention of base cations by plant uptake by comparing input and output.…”

Landscape factors of nutrient transport in temperate agricultural catchments

“…Even in sites with a natural or seminatural buffer zone between a nitrogen source area and a surface water body, a range of 0.01-142 kgN*ha -1 *y -1 [16,19,28,[33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] is reported to enter the water. The uppermost extreme values of more than 20 kgN*ha -1 *y -1 [19,[50][51][52] are probably fluxes from adjacent slopes without superaquatic buffer zones.…”