Heterogeneity in Urban River Ecosystems:

1. Heterogeneity in Urban River Ecosystems: Understanding the contribution of natural and anthropogenic factors on whole stream metabolism in ponded areas of the Ipswich River Watershed Joshua S. Cain Wil Wollheim • 1. Background • The Issue: Many reaches within the Ipswich River Watershed are characterized by low dissolved oxygen content, which threatens fish populations, aquatic organisms, and the health of the entire ecosystem. • Anthropogenic factors, including nutrient loading, road crossings, etc. and natural beaver dams found in this suburban watershed influence metabolism . • Little is known about the influence of fluvial wetlands on the dissolved oxygen, metabolism, and nutrient dynamics of a river network (O Brien et al. 2012). • Project Summary: This study will focus on understanding the interaction of geomorphology, dissolved oxygen, metabolism, and nutrients in a suburban river network. The project proposes to measure stream metabolism in natural and anthropogenically altered portions of a river network to better understand the influence of fluvial wetlands on dissolved oxygen content and metabolism rates observed downstream. • 4. Approach: • Overarching Approach:Dissolved oxygen, metabolism, and biogeochemical patterns will be measured continuously for weeklong periods at each study site during base flow conditions. • There will be 8 sites • Within each site, there will be 3 logger locations (sub sites) • one channel uninfluenced by fluvial wetland, one fluvial wetland (pool), one channel downstream of wetland • Seasonality will be addressed: measurements in spring, summer, fall. • Site Selection: • Encompass a variety fluvial wetland/ponds. (Figure 1) • beaver ponds, through-flow wetlands, back ups from culverts and debris dams, etc. • Metabolism Measurements: • Single Station Method • dDO/dt = GPP – R – A (Odum 1956) • Hobo DO loggers • above the ponded environment, just below the pond, and further down stream (channelized). • Odyssey light loggers will be placed in accordance with each DO logger. • Measurements will be taken every 15 min. • GPP and Respiration will be calculated based on the diel change in DO (Owens 1974). • re-aeration will be calculated using dark regression method (Young and Huryn 1999). • Site Characteristics: • Surface Area of water will be measured using either physical measurements, or GIS • Quantify the area each station is characterizing and investigate if the percent of DO depleted increases with pond area. • Discharge will be calculated to characterize the water movement at each site (flow meters? rating curve?) • Nutrients: • Grab samples will be taken 3 times per week to and tested for multiple constituents, including ammonium, anions (including NO3, SO4, and Cl), phosphate, dissolved organic carbon (DOC), and total dissolved nitrogen (TDN). • This will allow us to understand interactions between GPP, R, and nutrients. • 5. Preliminary Results (Chestnut site) • Dissolved oxygen steadily decreases along the transect from above the wetland to outflow of the lower wetland (Figure 2). Above Wetland (channel) Within Wetland (before culvert) Below Wetland (channel) Figure 2: Dissolved oxygen and temperature patterns at the Chestnut Site during October and into November Figure 1: Chestnut Street Site. Courtesy of Ken Sheehan • 6. Next Steps: • Identify Sites • Is the one station method going to highlight patterns observed in the entire pond, or do measurements need to be taken within the pond as well? • Transect sampling to understand why DO remains low even in channelized areas • 2. Research Question and Hypotheses: • Q1:What Is causing the extremely low dissolved oxygen content and high metabolic rates  observed in streams of the Ipswich river watershed? • Hypotheses: • Fluvial wetlands are extremely heterotrophic, driving down oxygen, while re-aeration in channels is low, keeping depressed oxygen levels over long reaches. • Humans are exacerbating this issue through road crossings with inadequate culverts, and water withdrawals, that are increasing inundation of fluvial wetlands, and reducing re-aeration rates. References: O’Brien, J. M., Hamilton, S. K., Kinsman-Costello, L. E., Lennon, J. T., & Ostrom, N. E. (2012). Nitrogen transformations in a through-flow wetland revealed using whole-ecosystem pulsed 15 N additions, 57(1), 221–234. doi:10.4319/lo.2012.57.1.0221 Odum, H.T. 1956. Primary production in flowing waters. Limnology and Oceanography 1(2):102-117. Owens, M., 1974. Measurements on non-isolated natural communities in running waters. In: Vollenweider, R.A. (Ed.), A Manual on Methods for Measuring Primary Production in Aquatic Environments. Blackwell Scientific Publications, Oxford, UK, pp. 111–119. Young, R. G., & Huryn, A. D. (1999). EFFECTS OF LAND USE ON STREAM METABOLISM AND ORGANIC MATTER TURNOVER. Ecological Applications, 9(4), 1359–1376 http://www.ourworldfoundation.org.uk/turbine.jpg - - background photo