EFFECTS OF CLIMATE AND AGRICULTURAL LAND MANAGEMENT ON LONG-TERM DEEP-WATER DISSOLVED OXYGEN DYNAMICS IN A PRODUCTIVE RESERVOIR

Many worldwide lakes show declining deep-water dissolved oxygen (DO) concentrations which may threaten ecosystem integrity by influencing biogeochemical processes, internal nutrient cycling, and suitable habitat availability. Declines in deep-water DO are largely associated with increasing air temperature or increasing nutrient inputs. Here, we use a 30 year dataset for Acton Lake, a hypereutrophic reservoir with watershed land use dominated by agriculture. Over this time period, air temperature has increased. Additionally, agricultural land management shifted toward increased conservation tillage, and concomitant decreases in sediment/nitrogen loads, early in the dataset while conservation tillage declined later in the dataset. It is within this context that we explore 1) long-term DO trends, and 2) drivers of interannual deep-water DO variability. Our results reveal that anoxia onset (i.e., day of year DO < 1 mg/L), and anoxic factor (AF) did not significantly change over time. However, anoxia onset and AF were associated with climatic factors and land management. In particular, anoxia onset occurred earlier in dry or warm springs while the AF increased with warmer summer air temperatures. Furthermore, increased conservation tillage was associated with earlier anoxia onset and greater AF suggesting that reduced sediment loads, a consequence of conservation tillage, may have elevated phytoplankton and heterotrophic respiration. Results highlight that the effects of a changing climate on lake DO may be masked by complex local factors such as shifts in farming practices.

Primary Presenter: Lesley Knoll, Miami University (knolllb@miamioh.edu)

Authors:

Lesley Knoll, Miami University  (knolllb@miamioh.edu)

Evan Youngblade, Miami University  (youngbe4@miamioh.edu)

Michael Vanni, Miami University  (vannimj@miamioh.edu)