Development of a Macroalgae Monitoring Protocol with Pilot Study for the Great Bay Estuary, N.H.
Eberhardt, A., D. Burdick, M. Dionne and R. Vincent. Rethinking the freshwater eel: salt marsh trophic support of the American eel, Anguilla rostrata. Estuaries and Coasts 38(4):1251-1261, July 2015.
Cianciola, E. (2014). Evaluation of macroalgae and options for macroalgal monitoring in Great Bay Estuary, N.H. Master's thesis, University of New Hampshire.
Survey in N.H.’s Great Bay confirms dramatic increase in algal abundance
Excess nitrogen in N.H.’s Great Bay Estuary can increase algal growth, which competes with and may stress rooted aquatic plants such as eelgrass. With funding provided by a N.H. Sea Grant development grant, researchers collected data in 2013 to evaluate the abundance of macroalgae in the estuary and found a dramatic increase from the results of surveys conducted 30 years ago, but similar levels to those found in 2008. These updated data results will help resource managers to better understand the extent of algal growth in the estuary for improved decision-making about nutrient management within the watersheds that drain into Great Bay.
Macroalgae sampling in N.H.’s Great Bay leads to development of long-term monitoring protocol
N.H.’s Great Bay Estuary is considered an impaired water body due to high levels of nitrogen since 2008. Excess nutrients, including nitrogen, increase algal growth that may impact native aquatic plants and animals in the estuary. N.H. Sea Grant-funded researchers conducted studies in the estuary to determine the abundance of macroalgae in the estuary. Transect sampling efforts created and vetted in 2013 during this project helped researchers to develop a macroalgae monitoring protocol that will be utilized for the estuary in 2014 and potentially long-term. This protocol will enhance macroalgae monitoring efforts, thus providing information related to biodiversity, climate change and water quality in the estuary.
New predictive models estimate biomass of common macroalgal species in N.H.’s Great Bay
N.H.’s Great Bay Estuary is considered impaired due to excess nitrogen, which can lead to an increase in macroalgal growth and cause subsequent negative impacts on native aquatic plants and animals in the estuary. N.H. Sea Grant-funded researchers conducted transect sampling surveys to determine the abundance of macroalgae in the estuary. Using these data, researchers developed linear regression models in 2013 that predict the biomass of six common macroalgal species based on ground cover estimates from the estuary. As improvements are made in the predictive ability of these models, they will allow researchers to use the ground cover data they collect to estimate algal biomass, thus eliminating the need to measure biomass empirically.
Description of Project
Eleven of the eighteen assessment zones in the Great Bay Estuary were listed as nitrogen-impaired in 2008 (NHDES, 2012). Because of the role that runoff plays in the nitrogen load to the Great Bay Estuary, any changes in nitrogen concentrations in the bay may reflect increasing populations and sewer discharge, land use changes upstream in the watershed, or changes in precipitation patterns due to climate change. Nitrogen fertilization can increase algal growth (Bricker et al., 2008), and the increased algae may stress both extant and restored eelgrass (Zostera marina L.) (Beem and Short, 2009). In 2010, researchers also observed that the abundance of macroalgae had increased dramatically (Nettleton et al., 2011) since the last study was conducted thirty years earlier. In response, the Piscataqua Region Estuary Partnership (PREP) adopted macroalgae abundance as one of its sixteen environmental indicators of the health of the Great Bay Estuary and is now in need of a monitoring plan that will collect the data needed to assess the status of this indicator. To help understand changes in the nitrogen loads and macroalgae populations of the estuary, the authors of this proposal ask the following questions:
What variation do habitat and nitrogen source create in the nitrogen isotope signatures of macroalgae in Great Bay?
What trends occur in macroalgal abundance in the Great Bay Estuary?
What shifts are occurring in the species composition of macroalgae in the Great Bay Estuary?
To answer these questions, the researchers will 1) design and implement an annual groundcover assessment and 2) analyze the nitrogen isotope ratios of macroalgae collected from a variety of microhabitats in the estuary. Measuring the N15: N14 ratios of macroalgae samples will allow the researchers to determine the contribution of human wastewater sources (high N15) to macroalgal growth relative to the contributions of other nitrogen sources, such as fertilizers and storm water runoff.
In accordance with New Hampshire Sea Grant’s current strategic plan, this research will help "develop methods for quantifying and predicting biological responses within coastal habitats." It is intended that the groundcover assessment will be able to provide the groundtruthing needed to support remote sensing efforts for eelgrass in the estuary. Sites from the two previous studies are to be retained from year to year in the annual assessments to allow for comparison with existing data.
After the pilot study, the annual groundcover assessment will be implemented by a team of experts and volunteers to provide data for the PREP to assess the health of the estuary in its State of the Estuary reports. The PREP is building funding to support a basic annual assessment into its next fiscal budget, but may not be able to cover the complete cost of the assessment. The researchers, the PREP, and the Great Bay National Estuarine Research Reserve intend that the annual groundcover assessment will become part of an integrated ecosystem assessment for the Great Bay Estuary in the future. A full research proposal will be written to support the integrated ecosystem assessment work.
Annual cover assessment: A random selection of 45 sites each for bare mud, eelgrass beds, saltmarsh cordgrass, and macroalgae will be used to assess cover in coordination with an aerial mapping effort in late August at spring tide. In addition, 20 sites in the pilot long-term study (described below), representing 10% of the total number of sites, will serve as permanent assessment sites. Sites will be located using GPS coordinates. Cover types (mud, eelgrass, cordgrass, macroalgae) within a 0.5 by 0.5 meter PVC quadrat will be estimated and recorded to the nearest of the following categories: 1%, 5%, 10%, or any multiple of 10% thereafter. With the quadrat in place, each site will be photographed showing a marker board with the site number and a scale.
Long-term pilot study: Establish three transects at each of five sites studied in 2010: 1) Great Bay Discovery Center, 2) Lubberland Creek, 3) Wagon Hill Farm, 4) Bayside Road, and 5) Hodgdon Farm Lane. Relocate existing plots and establish 1 transect through the center, marking sampling locations at -1, 0, 1, 2 m elevations relative to mean low low water (these are the 20 plots used in Annual cover assessment), and at the same elevations on two parallel transects 50 m on either side of the center transect.
Percent cover: Lay out a 0.5 meter x 0.5 meter PVC quadrat and visually estimate the percent of the ground covered by each species of macroalgae. Estimate one cover value for all cryptic species of Ulva.
Months: March, May, July, then every three weeks through November
Biomass: Lay out a 0.25 meter x 0.25 meter stainless steel frame 2 meters west of percent cover plot. Record percent cover by species using cover classes described for annual rapid assessment before collecting material from within the frame. Collect second sample immediately west of the first, third immediately south of the second, and fourth immediately east of the third. Use a set of tongs of the same dimensions to collect biomass from submerged sites. Rinse the samples under distilled water, dry them in an oven for 3 days at 90 degrees Celsius, and weigh the dry material.
Months: May, July, September, November
Nitrogen isotopes: Collect 12 individuals of each species observed in the percent cover squares of 3 of the randomly selected sites of each of the four cover types. Rinse samples under distilled water, dry them for 3 days at 60 degrees Celsius, and cut them into strips 2 centimeters long. Crush samples and run them through continuous flow isotope ratio mass spectrometry.
Months: Late August
Beem, N. and F.T. Short. 2009. Subtidal Eelgrass Declines in the Great Bay Estuary, NH-ME. Estuaries and Coasts. 32: 202-205.
Bricker, S., B. Longstaff, W. Dennison, A. Jones, K. Boicourt, C. Wicks, and J. Woerner. 2008. Effects of nutrient enrichment in the nation’s estuaries: A decade of change. Harmful Algae. 8: 21-32.
Nettleton, J., C. Neefus, A. Mathieson, and L. Harris. 2011. Tracking environmental trends in the Great Bay Estuarine System through comparisons of historical and present-day green and red algal community structure and nutrient content. Final Report to GBNERR, Durham, NH.
New Hampshire Department of Environmental Services. 2012. Draft 303d List. http://des.nh.gov/organization/divisions/water/wmb/swqa/2012/index.htm. 25 November 2012.