Nutrient cycling within the Meduxnekeag River and the use of periphytic algae as an indicator of nutrient loading

 

Abstract

A 20-mile segment of the Meduxnekeag River in Aroostook County, Maine, that traverses Houlton Band of Maliseet Indian (HBMI) tribal lands is experiencing substantial filamentous algal blooms in summer months. The algal blooms have lowered dissolved oxygen (DO) levels in the river to the extent that a 6-mile stretch within the segment has been deemed impaired by the Department of Environment Protection (DEP). Water chemistry data collected by the HBMI are available from 1995 to the present for this stretch of the river and indicate that the blooms may be phosphorus (P) limited, but that the algae are moderating stream chemistry and responding to flow dynamics to an extent that controls over algal production are unclear. A Watershed Protection Plan/Environmental Assessment for the Main Branch of the Meduxnekeag River was published in 1993, a Total Maximum Daily Load (TMDL) Report was published by the Department of Environmental Protection (DEP) in 2000, and the U.S. Geological Survey (USGS) is finalizing a sediment study it conducted this summer (2003). Currently, no research has linked the existing water quality data to nutrient dynamics in the river, or pinpointed the relative input contributions from point and non-point sources, of which there are many. These including unbuffered agricultural stream inputs, wetland, and lake recharge as well as industrial and wastewater effluent and proximity to impermeable surface inputs; all of these inputs are upstream of the Maliseet tribal lands. We propose to evaluate the underlying cause of the eutrophication by compiling and analyzing the existing data, investigating nutrient cycling in the river (including sediment and the water column), identifying nutrient loading areas and relative contributions of point and non-point sources, and determining temporal and spatial changes in the algae. Our overarching goal is to identify the causes of the problem, or to prioritize the likely causes, and thus provide supportive data that may lead to recommendations for remedy.

Statement of critical regional or state water problem:

Although environmental regulations have drastically reduced point source pollution, non-point source pollution remains a leading cause of water quality problems nationwide. State inventories indicate that agriculture impacts 48 percent of impaired rivers and streams (EPA, 2002). One of the major constituents of non-point source pollution is sediment, which is transported from agricultural and urban areas and carries heavy metals, pesticides, oils, and nutrients. High nutrient concentrations are a leading cause of impairment and eutrophication, a symptom of which is oxygen-depleting algal blooms.

The algal blooms in the Meduxnekeag River depress dissolved oxygen (DO) levels and alter the habitat of fish and other biota. Throughout the state, rivers are being altered to such an extent that they are losing native fish populations. Tribal members have observed non-native fish (bass, sucker, pickerel) becoming dominant while native trout numbers are declining (Ellis, pers. comm. 2003). The Maine State Planning Office’s River Study lists the Meduxnekeag River as having natural and recreational values of statewide significance. However, the algal blooms and resulting low DO levels are threatening this status. A 6-mile segment of the river downstream of Houlton is listed on the state’s 303d and 305b list for non-attainment of water quality standards because of high nutrient loads and low DO levels.

Although its presence on the impaired list legally requires corrective measures to be taken, so little is known about nutrient sources and cycling in the Meduxnekeag River that the any solution would be speculative at this point in time. Moreover, an evaluation of the Meduxnekeag River eutrophication, which is rare for Maine, will be useful for our understanding of processes statewide, because of increasing pressures on many Maine waters. Also, since the project will quantify the relative inputs from point and non-point sources, our research will be applicable to other areas with nonquantified point and non-point sources of nutrient enrichment.

Several states are battling eutrophication problems that became widespread before they were well understood, forcing a reactive approach; Maine, on the other hand, has an opportunity to be proactive and address the issue while it is still relatively small scale. We can gain an understanding of nutrient cycling in the river and use that knowledge to drive a restoration plan that will be a model for other areas of the state and beyond.

Statement of results and benefits:

This research will fill the gaps in the existing data and provide a portrait of nutrient loading and cycling within the river. It will also explore the use of periphytic algae as an indicator of nutrient loading. By linking temporal and spatial algal bloom data with the nutrient dynamics of the water column and sediment, the research can be used to target and further investigate problematic areas (i.e. major nutrient contributors) in the watershed. We will explore the possibility that isotope abundance of N in source waters and PS and NPS pollutants can corroborate stream chemistry in explaining algal production patterns.

Not only will the project serve as a model that can be applied to other rivers with nutrient enrichment problems, it can be used to help shape land use management within the Meduxnekeag watershed. HBMI was awarded a Watershed Initiative Grant during summer 2003 to improve water quality in the watershed, and a large portion of the grant is appropriated to working with farmers to decrease erosion and non-point source pollution resulting from agriculture. Our proposed research complements that grant by indicating relative input contributions and identifying problem areas that need extra attention. This research is the essential first step in a process that could restore the aesthetic and recreational value of the river, remove the river from the state’s impaired list, and reduce dangerous DO levels currently threatening the river’s biota.