River phosphorus cycling: Separating biotic and abiotic uptake during short-term changes in sewage effluent loading

• Published in: Water research (Oxford) Vol. 44; no. 15; pp. 4425 - 4436
• Main Authors: Stutter, M.I., Demars, B.O.L., Langan, S.J.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.08.2010; Elsevier
• Subjects: Algae; Algal assays; Applied sciences; Bacteria; Bacteria - growth & development; Bacteria - metabolism; Biological; Continental surface waters; Cycles; Ecosystem; Ecosystems; Effluents; Environmental Monitoring - methods; Eukaryota - growth & development; Eukaryota - metabolism; Exact sciences and technology; Freshwater; General purification processes; Geologic Sediments - analysis; Geologic Sediments - chemistry; Kinetic sorption studies; Natural water pollution; Nutrient spiralling; Open flow-through columns; Other industrial wastes. Sewage sludge; Phosphorus - analysis; Pollution; Rivers; Rivers - chemistry; Sewage - analysis; Sewage - chemistry; Stoichiometry; Streams; Time Factors; Uptakes; Wastes; Wastewaters; Water Microbiology; Water Pollutants, Chemical - analysis; Water treatment and pollution; Whole stream metabolism; Stoichiometry; Open flow-through columns; Algal assays; Whole stream metabolism; Kinetic sorption studies; Nutrient spiralling; Short term; Radioactive pollution; Radioisotope; Waste water; Batchwise; Ecosystem; Watershed; Bacteria; Stream; Biocide; Point source; Algae; Phosphorus; Metabolism; Sediments; Sorption; Surface water; Biofilm; Kinetics; Material balance
• ISSN: 0043-1354; 1879-2448
• DOI: 10.1016/j.watres.2010.06.014

Medium to small scale point sources continue to threaten river ecosystems through P loadings. The capacity and timescales of within-river processing and P retention are a major factor in how rivers respond to, and protect downstream ecosystems from, elevated concentrations of soluble reactive P (SRP). In this study, the bio-geochemical response of a small river (∼40 km 2 catchment area) was determined before, during and after exposure to a fourteen day pulse of treated sewage effluent using an upstream reach as a control. A wide array of approaches (batch and column simulations to in-situ whole stream metabolism) allowed independent comparison and quantification, of the relative contribution of abiotic and biotic processes in-river P cycling. This enabled, for the first time, separating the relative contributions of algae, bacteria and abiotic sorption without the use of labelled P (radioisotope). An SRP mass balance showed that the ecosystem switched from a P sink (during effluent inputs) to a P source (when effluent flow ceased). However, 65–70% of SRP was retained during the exposure time and remained sequestered two-weeks after-effluent flow ceased. Batch studies treated with biocide gave unrealistic results, but P uptake rates derived by other methods were highly comparable. Downstream of the effluent input, net P uptake by algae, bacteria and sediment (including the biofilm polysaccharide matrix) were 0.2 (±0.1), 0.4 (±0.3), and 1.0 (±0.9) mmol m −2 day −1 during effluent exposure. While autotrophic production did not respond to the effluent exposure, heterotrophic production increased by 67% relative to the control and this translated into a 50% increase in biological P uptake rate. Therefore, both biological and abiotic components of stream ecosystems uptake P during exposure to treated sewage effluent P inputs, and maintain a long ‘memory’ of this input in terms of P storage for considerable timescales after loading.