Factors that control the spatial and temporal distributions of phosphorus, nitrogen, and carbon in the sediments of a tropical reservoir

Abstract

The impacts of anthropic activities have had profound effects on the nitrogen (N) and phosphorus (P) cycles in many aquatic ecosystems. We investigated the spatial and temporal distributions of carbon (C), N, and P in the sediments of a tropical Paiva Castro Reservoir (São Paulo, Brazil), as well as their release and retention in the system. In 2010, surface sediments were collected at nine sites in the reservoir, and a core was obtained in the limnetic zone, in 2010. The core was dated using the Pb technique. The organic C content was estimated from organic matter concentration, which was measured by the loss-on-ignition method, and the concentrations of P and N were determined by spectrophotometry. Marked spatial heterogeneity in the Paiva Castro sediments associated with both natural variations in the water body and variations induced by human impacts was observed. Heterogeneity was evidenced by a decrease in the allochthonous contribution of organic matter (C/N) in the upstream-downstream direction and increases of N and P, mainly associated with water flows in the different compartments of the reservoir. In the core, C and N concentrations display significant positive correlations with increases in population and agricultural activities in the drainage basin through time. The C/P molar ratios in surface sediments are indicative of human impacts in the region, as C:P ratios in the sediment are low (7.8:1) compared to the Redfield ratio (C:P = 108:1). Predominance of oxic conditions at the sediment surface and particles sizes< 63 μm provided favorable conditions for P retention in the sediments, which helps prevent eutrophication. Approaches used in this research should be extended to other locations, especially in mesotrophic and oligotrophic reservoirs, to provide information on historical impacts in such aquatic ecosystems.

Land-Cover Patterns and Hydrogeomorphology of Tributaries: Are These Important Stressors for the Water Quality of Reservoirs in the Mediterranean Region?

“…The link between LULC and EC pore-water values is consistent with other studies that reported positive correlations between this parameter and intensive agriculture activities and urban classes [7,52]. Further, streams surficial sediments were characterized as inorganic, with mean percentages of organic matter (OM) contents less than 6 [53]. Table 1.…”

High Inter- and Intra-lake Variation in Sediment Phosphorus Pools in Shallow Lakes

“…In fact, the depth of the water at the sediment sampling location described the vast majority (84.1%) of the variation in looselybound P and over half of the variation (63.1%) in total P concentrations. The pattern of higher concentrations at greater depths is likely driven by sediment focusing and greater net sediment deposition in deeper portions of the lake (White & Stone, 1996;Hou et al, 2014;Cardoso-Silva et al, 2018). The direct relationship that we observed between water depth and sediment P concentrations is consistent with other studies of spatial variation in sediment P pools (Nowlin et A factor that may influence the spatial distribution of the sediment P pool is the location and density of macrophyte beds.…”

“…The spatial distribution of the sediment P pool is also heterogeneous within individual shallow lakes following variation in sediment transport, deposition, and resuspension processes (Mackay et al, 2012). Sediment total P generally increases with water depth as a result of sediment focusing, which concentrates fine-grained, P-enriched sediments in deeper portions of the lake basin (White & Stone, 1996;Hou et al, 2014;Cardoso-Silva et al, 2018). Dynamic disturbance and biological activity across the lakebed further drive spatial variation in sediment P speciation in shallow waterbodies (Forsberg, 1989;Nowlin et al, 2005;Kowalczewska-Madura et al, 2019a).…”

Water-Sediment Physicochemical Dynamics in a Large Reservoir in the Mediterranean Region under Multiple Stressors

“…Surface sediments of the Alqueva reservoir are mainly inorganic, with OM contents < 12% [67]. Despite the high variability of TPs concentrations, much influenced by oxic conditions, pH and iron forms [68], all the sediments presented concentrations of TPs higher than the severe effect level (TP SEL > 0.2%; [69]), classifying the sediments as heavily polluted, and likely to affect the health of sediment-dwelling organisms. Montante was the location with the highest concentrations of TP s , achieving values of 17.5% in the wet period for both years.…”