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Aquatic macrophytes in an agricultural drainage ditch were able to accrue large amounts of nitrogen (N) and phosphorus (P) during the growing season and held these nutrients until tissue breakdown in autumn. Total nutrient accumulation by aquatic macrophytes in a 1.4 km (8612 m2) ditch was 49.0 kg N (5.65 mg N m−2) and 11.0 kg P (1.29 mg P m−2). Release of these nutrients upon tissue breakdown was rapid. Average breakdown rates, based on ash-free dry mass (AFDM) loss, for Elodea canadensis and Potamogeton nodosus were 0.0615 ± 0.0450 d−1 (r2 = 0.788) and 0.0260 ± 0.0170 d−1 (r2 = 0.688), respectively. Time required for 95% loss of plant tissue (T95 = 3/k) was 49.0 days for Elodea and 116.9 days for Potamogeton. Nitrogen and phosphorus losses from decaying plants closely followed AFDM losses. Mass balances for N and P indicated the 94% of the N and 72% of the P accumulated by aquatic macrophytes were obainted from surface sediments. Sediment N and P pools were 864 kg and 62 kg, respectively.
aquatic macrophytes, nitrogen, phosphorus, sediment, docomposition, drainage ditch, stream, nutrient budgets
Assistant professor, Graduate Program in Environmental Sciences, University of Texas at Dallas, Richardson, TX