| Project
summary:
Estuarine
environments, some of the most productive and important
coastal habitats, are often the primary recipients
of landscape-derived nutrients and pollutants from
agricultural and urban development of the coastal
zone. Our growing population creates ever increasing
demands on the embanked floodplain shores of our estuaries.
Sustainable development of these resources necessitates
further understanding of the complex water-terrestrial
interactions occurring both in space and time.
This research
focused on four questions pertaining to estuaries
in the Virginian Biogeographic Province (Cape Cod
to Cape Hatteras): (1) are measures of estuarine water
quality the same across study regions; (2) are spatial
setting variables and intense rainfall events important
in explaining variation in water quality measures;
(3) what is the relationship between patterns of land
cover and estuarine condition; and (4) is land cover
change a good regional indicator of water quality
condition for these diverse estuaries.
Estuarine
data were extracted from the Environmental Monitoring
and Assessment Program (EMAP) and Coastal-2000 surveys.
Geographic Information System’s (GIS) neighborhood
modeling, land-use/cover change detection of remotely
sensed data, cumulative distribution functions and
multiple linear regression analyses were used to quantify
land - estuarine water quality interactions in three
regions representing urban and agricultural gradients
along the our research area.
Description
of distributions of water quality indicators weighted
by estuarine area for each region showed a close relationship
between land use and the measure of water quality
in surrounding estuarine areas. For example, the estuarine
area in the highly urbanized Hudson/Raritan region
contained the largest proportion of low dissolved
oxygen and exhibited the higher levels of sediment
contaminants. Spatial setting variables accounted
for the effect of location on measurements of estuarine
condition. They were used as surrogate variables of
estuarine factors not included in the models (i.e.,
tidal currents, residence time). After removing for
spatial-effects from estuarine condition data, weak
but significant relationships were found between total
urban area and water quality indicators for the three
regions. Biological response, measured by the Benthic
Index (EMAP), was significantly explained by de-trended
estuarine data. It was also inversely related to total
organic carbon, silver, and arsenic in the sediments;
while showing a positive relationship to salinity
and temperature.
Our results
show that: (1) estuarine water quality measures differ
among study regions by testing cumulative distribution
functions of indicators of water quality within and
among regions; (2) spatial setting variables and intense
rainfall events explain some of the variability in
water quality measures; (3) by removing the spatial
effect from estuarine condition data, landscape metrics
of total urban areas within a 4-km buffer explain
a small, but significant amount of variation in indicators
of eutrophication and sediment metals in the composite
of three regions. On a regional basis, both urban
settings and agriculture have a significant effect
in Cape Cod where they explained from 12 to 38% of
the variation in sediment metals and organics; and
(4) benthic community status in the Cape Cod, Hudson/Raritan,
and Delmarva regions, was explained by the Benthic
Index relationships to sediment metals and physical
conditions such as salinity and temperature.
The effect
of spatial setting on indicators of estuarine condition
was strikingly high in Delmarva, where distance-to-shore,
oceanic and riverine categories significantly explained
variability of sediment organics including Fluorant,
Dieldrin and PCBs. Lagoonal locations also had a significant
negative effect on arsenic, cadmium, and lead, explaining
between 32 to 53% of their variation. After removing
spatial setting effects from indicators of estuarine
condition, we found that effect of land cover change
on water quality showed clear pattern differences
between Delmarva and the other two regions during
the 1984-1992 period.
In Delmarva,
land cover change in buffer zones located 6, 8, and
10-km from monitoring stations had a significant effect
on the Benthic Index and measures of silver, arsenic,
cadmium, and mercury. In Cape Cod, land cover change
in the same buffer zones explained approximately 15%
of the variation in PHs, dissolved oxygen, and silver.
There was no effect of land cover change between 1992-1999
in estuarine condition in Cape Cod and Delmarva, and
significant effect in the Hudson/Raritan region. |
