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Agricultural runoff carries high nutrient loads to receiving waters, contributing to eutrophication. Managed wetlands can be used in integrated management efforts to intercept nutrients before they enter downstream aquatic systems, but detailed information regarding sorption and desorption of P by wetland sediments during typical inundation cycles is lacking. This study seeks to quantify and elucidate how inundation of wetland sediments affects bioavailability of P and contributions of P to downstream systems. A managed wetland cell in Tunica County, Mississippi was subjected to a simulated agricultural runoff event and was monitored for bioavailable phosphorus (water-extractable P [P], Fe-P, and Al-P) of wetland sediments and water level during the runoff event and for 130 d afterward. Inundation varied longitudinally within the wetland, with data supporting significant temporal relationships between inundation and P desorption. Concentrations of P were significantly higher at the site that exhibited variable hydroperiods (100 m) as compared with sites under consistent inundation. This suggests that sites that are inundated for longer periods of time desorb less P immediately to the environment than sites that have periodic or ephemeral inundation. Concentrations of iron oxalate and NaOH-P were significantly higher at the least inundated site as compared with all other sites (F = 5.43; = 0.001) irrespective of time. These results support the hypothesis that increased hydraulic residence time decreases the bioavailability of P in wetland sediments receiving agricultural runoff. This finding suggests that the restoration of wetlands in the mid-southern United States may be hydrologically managed to improve P retention.

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Watershed-scale management efforts to reduce nutrient loads and improve the conservation of lakes in agricultural watersheds require effective integration of a variety of agricultural conservation best management practices (BMPs). This paper documents watershed-scale assessments of the influence of multiple integrated BMPs on oxbow lake nutrient concentrations in a 625-ha watershed of intensive row-crop agricultural activity during a 14-yr monitoring period (1996-2009). A suite of BMPs within fields and at field edges throughout the watershed and enrollment of 87 ha into the Conservation Reserve Program (CRP) were implemented from 1995 to 2006. Total phosphorus (TP), soluble reactive phosphorus (SRP), ammonium, and nitrate were measured approximately biweekly from 1996 to 2009, and total nitrogen (TN) was measured from 2001 to 2009. Decreases in several lake nutrient concentrations occurred after BMP implementation. Reductions in TP lake concentrations were associated with vegetative buffers and rainfall. No consistent patterns of changes in TN or SRP lake concentrations were observed. Reductions in ammonium lake concentrations were associated with conservation tillage and CRP. Reductions in nitrate lake concentrations were associated with vegetative buffers. Watershed simulations conducted with the AnnAGNPS (Annualized Agricultural Non-Point Source) model with and without BMPs also show a clear reduction in TN and TP loads to the lake after the implementation of BMPs. These results provide direct evidence of how watershed-wide BMPs assist in reducing nutrient loading in aquatic ecosystems and promote a more viable and sustainable lake ecosystem.

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Watershed-scale management efforts to improve conservation of water resources in agricultural watersheds depend upon the effectiveness of integrated multiple agricultural best management practices (BMPs). To more comprehensively assess the effectiveness of combined BMPs on water quality requires large-scale, long-term (>10 year) studies measuring key water quality parameters. One such suite of critical water quality parameters includes water clarity, total suspended solids (TSS), and total dissolved solids (TDS). To address this, Beasley Lake, a 25 ha (62 ac) oxbow lake located in a 915 ha (2,261 ac) watershed of intensive row crop agricultural activity, was studied. The lake was sediment impaired when monitoring was initiated in 1995 and was a candidate to assess the effectiveness of watershed-wide BMPs on lake water clarity (as Secchi depth), TSS concentrations, and TDS. A variety of BMPs within row crop fields, at field edges throughout the watershed, and enrollment of 112 ha (277 ac) into the Conservation Reserve Program (CRP) between 1997 to 2006 focused on reducing soil erosion and concomitant sediment runoff. Selected parameters were measured approximately biweekly from 1996 to 2009. During this 14-year period, changes in row crop management and BMP implementations and alterations were observed and recorded in conjunction with targeted water quality parameters. While annual improvement in water quality occurred, distinct seasonal effects were noticeable. Observed changes in water clarity and TSS concentrations were greatest during spring and least in winter in association with increased BMPs, vegetated buffer strips west of the lake, and CRP north of the lake. Observed decreases in TDS concentrations were greatest during summer and fall in association with implemented CRP north of the lake. Reductions in spring TSS by >60% often directly increased spring water clarity by >100%. Results of this study indicate clear improvement in lake water quality with watershed-wide implementation of integrated multiple agricultural BMPs, and these improvements, manifested most strongly during spring, will assist to promote a healthy, sustainable lake ecosystem.Key words: best management practices-oxbow lake-Secchi depth-total dissolved solids-total suspended solids Intensive row crop agriculture under conventional farming practices utilizes most available arable land. While necessary to feed and clothe a continually growing human population, these practices can often lead to significant soil erosion (Bennett and Chapline 1928) and surface runoff during rainfall events that produce increased loads of suspended sediment and dissolved solids, and decrease water clarity (Dodds and Whiles 2004;Renwick et al. 2008). Despite decades of research and considerable efforts to mitigate suspended sediment loading, suspended sediment continues to be one of the most pernicious pollutants and a significant cause of water quality impairment globally. Suspended sediment has long been known to cause problems in physical terms th...