Abstract
Greenhouse gases were sampled during spring and summer months in 2010 and 2011 at two sites in the Mississippi River Basin: a riparian forested wetland under restored flood pulsing near Memphis, TN and a coastal estuarine marsh complex impacted by a river diversion at Caernarvon, LA. Mean methane fluxes at Caernarvon (-0.09 g CH4-C m-2 d-1) were lower than those at Memphis (0.53 g CH4-C m-2 d-1), and did not differ between seasons. Nitrous oxide fluxes were generally below detection limits. Fluxes were uncorrelated with water depth, soil temperature, and ambient air temperature, though sampling occurred over a narrow range of these variables due to limitations in site accessibility. A water quality dataset spanning 8 years of monthly sampling was analyzed to determine long-term spatial and temporal patterns in nutrient concentrations at Caernarvon. The estuary served as a source of ammonium, and chlorophyll a and a sink for nitrate, total nitrogen and total suspended sediments. Classification of the estuary as a source or sink for phosphate, total phosphorus and silicate changed with the seasons. Nitrate removal efficiency varied seasonally, with efficiency highest in the fall (98%), summer (92%) and spring (87%) and lowest in the winter (74%). Removal efficiency was inversely related to loading rate. Water quality samples were collected at Memphis in a secondary channel of the Mississippi River under restored hydrology during spring and summer 2010-2011. Seasonal variations existed in concentrations of nitrate, total nitrogen, total phosphorus and total suspended solids, but not ammonium, phosphate, silicate, dissolved oxygen and chlorophyll a. No parameters varied longitudinally or laterally within the channel. Nitrate loading rate was high and removal efficiency was low, especially in comparison with Caernarvon and other study sites within the Mississippi River Basin, due to the limited size of the receiving wetland.
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