Continuous and Spatially Distributed Dissolved Oxygen Monitoring in Long Island Estuaries in Support of Coastal Resource Management.

Science Center Objects

Problem Dissolved oxygen (DO) is an important indicator of water quality that until recently has been cost-prohibitive to monitor extensively in both space and time. Continuous water-quality data, particularly in coastal environments with bidirectional tidal flow, is necessary for resource managers to understand the dynamic changes in water quality that occur tidally, daily, seasonally, and du...

Problem

Dissolved oxygen (DO) is an important indicator of water quality that until recently has been cost-prohibitive to monitor extensively in both space and time. Continuous water-quality data, particularly in coastal environments with bidirectional tidal flow, is necessary for resource managers to understand the dynamic changes in water quality that occur tidally, daily, seasonally, and during aperiodic events. In the estuaries surrounding Long Island, such events may include wastewater treatment plant failures, harmful algal blooms, and extreme weather. The U.S. Geological Survey (USGS) has extensive experience with continuous water-quality monitoring at fixed locations along the coast that provides valuable information which is served in real-time; however, data are limited spatially.

Low DO concentrations limit the survival of some economically and ecologically valuable species, such as the hard clam.  For this reason, investments for restoration of these species without fully understanding the local water-quality conditions can result in an unsuccessful restoration effort. Continuous and spatially distributed water-quality data are critical for regulatory agencies and stakeholders to support informed decisions in managing aquatic resources. Specifically, the proposed DO monitoring would provide more complete and accurate information to aid in the classification of water-quality impairments associated with Long Island estuaries as tabulated in the New York State Department of Environmental Conservation (NYSDEC) Waterbody Inventory and Priority Waterbodies List. This list aims to describe water quality and supported water uses, identify problems, and prioritize restorative measures.

Objectives

The primary objectives of this proposed project are to (1) collect continuous and spatially-distributed DO data and to make these data available in a publically-accessible database to inform regulatory agencies, stakeholders, and the public about water-quality conditions relevant to areas of concern, and (2) establish a baseline of DO concentrations, which will enable evaluation of wastewater improvement projects, the impacts of major coastal storms, and investments made toward improving water quality and restoring habitat and fisheries. 

Relevance and Benefits

This study will directly benefit government regulatory agencies, such as the NYSDEC, and other resource managers by advancing the knowledge of water-quality conditions spatially and temporally in key estuarine habitats. These publically accessible, quality-assured data will be housed in national databases and used to understand changing hydrologic conditions in support of coastal resource management.  This project would also serve to advance the capabilities of the USGS in the implementation of spatially-expansive, continuous coastal water-quality monitoring and would support the USGS goal of developing a distributed, rapid-response water-quality network aimed at improving coastal resiliency during major storms and other emergencies.

Approach

Stony Brook University School of Marine and Atmospheric Science (SoMAS) recently began a seasonal continuous monitoring program with DO sensors that have been deployed along the coast (accessible by land) in several locations across Long Island. The Nature Conservancy (TNC) plans to expand this network to include DO sensors deployed in transects across embayments with ecological concerns.  The USGS proposes to oversee data collection and management of the combined network according to published guidelines and make the data publicly available on the NWIS Web site (National Water Information System: Web Interface).

Key aquatic habitats that are/would be negatively impacted by wastewater and extreme weather (for example, seagrass beds), areas with historical distributions of juvenile hard clams, and areas with recurrent harmful algal blooms will be identified and considered for seasonal monitoring (June-September). Three new sites will be selected by TNC to be deployed as one transect in addition to reoccupying 10 of the 22 land-based sites that SoMAS monitored last year. These sites are distributed among the north and south shores of Long Island and along the Peconic Estuary. Continuous (6-min-interval) measurements of DO will be collected using Onset HOBO U-26 probes.  Specific conductance (SC) sensors will be deployed in parallel to DO with data collected at the same interval using the Onset HOBO U24-002 at sites with salinity changes of 2 ppt or greater. Sites where salinity changes are <2 ppt will have SC/salinity measured during servicing with a handheld meter. All data will be collected from 0.5 m above the seabed except for TNC sites that will have one sensor at 0.5 m above the seabed and one located just above the sediment surface in the same location for a vertical profile. Sensors deployed in transect will be housed in a copper pipe welded to a copper sleeve that slides over a galvanized helical screw anchor.  The copper pipe will be open ended so that the sensor can protrude to allow free-flow of water to the sensing end. Anchors will be jetted in with a water pump and located next to a set of surface markers (bamboo stakes) with a tether between them for quick identification.   Sensors installed from the shore will be deployed via steel cable to non-floating docks.  Sites are designed for quick initial deployment and easy removal after the monitoring season. The raw DO data will be processed using the SC record and the HOBOware Dissolved Oxygen Assistant software to adjust for salinity. All DO and SC sensors (with published record) will be serviced in accordance with guidelines described by Wagner and others (2006). Sensors will be serviced approximately every 10 days or 12 times during the season. Continuous SC record that will be collected solely for the purpose of DO corrections and not published to NWIS Web may have sensors cleaned and the calibration checked at longer service intervals depending on the extent of fouling.

References 

Wagner, R.J., Boulger, R.W., Jr., Oblinger, C.J., and Smith, B.A., 2006, Guidelines and standard procedures for continu­ous water-quality monitors—Station operation, record computation, and data reporting: U.S. Geological Survey Tech­niques and Methods 1–D3, 51 p. + 8 attachments; accessed April 10, 2006, at http://pubs.water.usgs.gov/tm1d3