Understanding the contribution of natural and anthropogenic factors to low dissolved oxygen in rivers of the Ipswich River Watershed

Low dissolved oxygen (D.O.) is an important water quality concern affecting fish populations in the Ipswich Watershed, draining to the Plum Island Estuary in northeastern MA. DO is determined by aquatic metabolism (GPP, Respiration) and re-aeration, each of which are potentially altered by human activities.  Recent measurements show that dissolved oxygen levels (% DO) are low in sections of the upper portions of the watershed, including headwaters and upper main stem. In some areas, DO levels drop to 0 percent saturation, and remain at low levels for a significant length of stream. We hypothesize that numerous wetlands in the headwaters of the Ipswich contribute to the low levels, while recent rebound of beaver populations, and anthropogenic changes associated with increased urbanization  (road crossings, dams, flow frequency, nutrients, water withdrawals), exacerbate the problem.  The increased abundance of pools, caused by under sized culverts, beaver dams, etc, causes decreases in flow, increased organic matter buildup, and higher water levels, which creates additional hydrologically connected riparian wetlands. These areas of high organic matter content have high oxygen demand, and therefore decrease the amount of dissolved oxygen in the water column and prevent re-aeration.

My future research aims to tease apart the relative importance of natural and anthropogenic factors as influences on organic matter dynamics and dissolved oxygen in surface waters of the Ipswich River watershed.  I plan to measure dissolved oxygen and metabolism in natural and anthropogenically altered portions of the river network.  Measurements will take place in channelized and pooled/wetland areas to determine how dissolved oxygen content changes as water passes through different types of hydrologic features.  Ancillary measurements will be made to understand the influence of various driving factors on metabolism and dissolved oxygen conditions.  Interactions of dissolved oxygen and other ecosystem processes such as nutrient uptake will also be explored.  This poster will present preliminary ideas and approaches for addressing this issue.