Geoscience Reference
In-Depth Information
degradation to the Tribs' fish communities. IBI scores below 20 are not usually seen
in areas where degraded habitat is the sole problem. Scores will generally descend
below 20 only when a watershed has been impacted by toxic effects of land use or
point sources of pollution, resulting in the loss of large portions of fish communities
and reduced biomass (
OEPA 1998
). Assuming that the threshold of 20 can be
applied to the study area, 14 sites in the study area have IBI scores below the
threshold for toxic impacts, with a few sites showing scores as low as 12 and 6.
Without a history of industrial point source pollution in the Tribs the question
arises: what may be contributing to the apparent toxic effects in the Tribs? If low
IBI scores are due primarily to the input of toxins via non-point source pollution
from agriculture, then the abundance of habitat is not likely to improve IBI scores.
Rather, altering farming practices to include significant reductions in chemical
fertilizers and pesticides may help improve biotic integrity.
Aside from agriculture, other land cover types likely have varying effects on
biotic integrity. Although impervious surfaces were not a significant predictor of
IBI or QHEI, effects may be missed due to the fact that the majority of impervious
surfaces within the study area fall outside of the 500 m buffers that were used for
analysis. Forest and wetland land cover types have been shown to have mitigating
effects on water quality (Wang et al.
1997
) in the form of sediment retention,
providing habitat, thermal control. Forested areas represent roughly 8% of total
land cover and water/wet vegetation about 4%. However, in the Tribs watersheds,
the distributions of these land cover types are so fragmented they may be providing
only minimal habitat functions. Although grassy areas were predicted to have a
weak negative correlation with IBI and QHEI, no relationship was found after
excluding water/wet vegetation from the analysis. This is despite the fact that grass
is the second most dominant land cover in the study area. The negative associations
of grass with modified landscapes may be negated by its function in erosion control.
Bare soil, also an indicator of residential development and only a minimal propor-
tion (2%) of total land cover, was not a predictor of biotic integrity or habitat.
In addition to land use, many other conditions within the Tribs watersheds have
made contributions to the current conditions. Channel slope, total drainage area,
flow velocity and spatial scale are all important considerations when attempting to
quantify land/water interactions. It has also been suggested that in addition to land
cover analyses, landscape patterns such as patchiness, average patch size, connec-
tivity, etc. are important in understanding the processes that influence water quality
and biotic integrity (Gergel et al.
2002
; Wiens
2002
). Another important factor is
the influence of seasonality, specifically the seasonal fluctuations in avian preda-
tion. The Ohio EPA fish surveys were conducted in late summer when evaporation
is high in NW Ohio. During this time, small sections of streams may begin to run
dry, providing an easily accessible fish community for birds, resulting in few
available samples for calculating IBI scores. Seasonal predation may have a larger
influence in the Tribs than in the other streams in the Maumee AOC due to their
relatively small size and lack of riparian canopy in many areas.
Overall, the datasets used for this study were extremely informative. The use
of secondary data provided a cost effective means for examining land cover/biotic
