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The Problem
Although the importance of the estuary to salmon and other species is becoming appreciated, there are substantial gaps in our understanding of estuarine ecology, and thus in our ability to interpret change and rank management alternatives. Relatively little is known, for example, about how primary production and higher trophic levels in the estuary have responded to man's activities upstream, and whether observed changes have been gradual or occurred during "regime" shifts on scales of 20-30 years. Little is known about how dam construction, land and water management, and rising human populations might be influencing conditions in an estuary. Changes in estuaries are occurring through varying nutrient levels, introduction of exotic species, contaminants, or other factors. Understanding and quantifying the historical variation in estuarine conditions could help to decipher what changes might be cyclical, which are likely human-caused, and which might be positively influenced by active management. A fruitful approach to studying long-term changes in aquatic ecosystems has been through the use of sediment cores and the types of indicators that can be extracted from these cores. Cores have been taken in oceans, lakes, reservoirs, and wetlands and used to examine shifts in primary producers, fish populations, and trophic structure. The accretion rates of organic and inorganic material can be determined from cores, and isotope ratios of Nitrogen, Carbon, and other elements can provide clues about changes in vegetation types (e.g., upland vs. riparian vs. emergent marsh versus plankton) or marine-derived nutrients. Temporal sequences of diatom casts, invertebrate structures, and plant pigments can be extracted from cores using established methods. Strata in cores can be aged, so changes following specific events, such as dam construction or contaminant spills, can be inferred, and trends in core measurements can be correlated with time series of water temperature or climate indices. Objectives The objective is to provide data that will better enable scientists and managers to understand the longterm variation in estuarine ecosystems. Such understanding may lead to better management through appreciation of regional mechanisms that are driving changes. Methodology
A number of cores were collected in the estuary of the Columbia River (Northwest USA) for this pilot study. The Columbia River is the largest river entering the northeast Pacific Ocean, draining a watershed of over 660,000 km2 that includes portions of seven U.S. states and two Canadian provinces. Samples were collected with a 7.5 cm diameter aluminum pipe that was driven into soft sediment bottoms. Cores were returned to the laboratory, sliced in half, and sectioned. Sediments within each core sections were aged using Lead and Cesium isotopes. Sediments were also examined for grain size, algal pigments, diatoms, and heavy metals. Highlights and Key Findings
At this time, three cores from the Columbia River estuary have been aged and analyzed. Aging suggests that the deepest sediments in the cores were laid down during the early 1900's, with fairly steady sedimentation through the last century. We have detected significant patterns of change through time in the algal pigments, diatom community, and in heavy metal concentrations. Where Are We Headed In 2003 This has been a pilot study to see if we could age sediments and detect useful indicators of the aquatic community. We have had success in these areas and will continue to analyze the current dataset. Patterns of change will be correlated across the three available cores to see if changes might have been caused by large-scale changes in the basin. Future work will include additional cores from other areas, and perhaps other estuaries, to better characterize the aquatic community and the factors that are causing changes. Project Contact Alec Maule Email: alec_maule@usgs.gov Publications |
