BEAVER POND BIOGEOCHEMISTRY - ACID NEUTRALIZING CAPACITY GENERATION IN A HEADWATER WETLAND

A beaver pond and its associated inlet and outlet waters in the Adirondack Mountains of New York were monitored for major chemical solutes for 26 months in an effort to quantify underlying chemical controls on the production and consumption of acid neutralizing capacity (ANC). The pond was a net annual sink for inlet Al, SO42-, NO3-, and H4SiO4. The pond was a net annual source of dissolved organic carbon (DOC), NH4+, and Fe2+. Losses of ANC resulting from Al and basic cation retention, as well as organic anion release (RCOO-) associated with DOC, were more than offset by SO42- and NO3- retention and Fe2+ and NH4+ release, resulting in a net production of ANC. Rates of ANC generation were 120 meg m(-2)yr(-1) and 310 meg m-2yr(-1), respectively (based on pond surface area), for the non-summer (October-June) and summer (July-September) periods. Seasonal variations in ANC in the outlet stream were largely associated with Fe2+ and DOC release, while ANC in the upland inlet stream was associated with Al, NO3-, and basic cations, with much less seasonal variation. Controls on stream chemistry were temporally and longitudinally different for the inlet and outlet streams. The shift to seasonal control of outlet stream ANC by processes associated with organic matter decomposition reactions and anaerobic zone nutrient transformations may be characteristic of headwater wetlands in temperate zones with seasonal temperature extremes. Beaver impoundments and wetlands may also be important in the upstream mobilization or retention of geologically bound solutes like Al, Fe, and H4SiO4. Headwater wetlands, as sinks for solutes associated with acidic deposition and watershed acidification (i.e., SO42-, NO3-, and Al), may play a role in the amelioration of the effects of these solutes on downstream receiving waters and associated biota. Depending on their location in relation to drainage patterns, these ponded systems may influence the nutrient dynamics of receiving waters through nitrogen transformations and organic carbon cycling.