Does land use affect stream water quality in the North Branch Park River watershed?

Background/Question/Methods

Land use and water quality are unequivocally linked.  With the growing
population and urbanization, water quality becomes impaired in the immediate
stream and downstream due to vast increases in commercial and residential
development, non-point source pollution, wastewater treatment effluent and
combined sewer overflows.  Collectively, these describe the urban stream
syndrome.  However, the impacts of land use on water quality may be site
specific.  The North Branch Park River (NBPR) watershed contains many urban
streams, which are susceptible to urban stream syndrome.  The watershed is
an approximately 29-square mile sub-regional basin within the Connecticut
River basin.  Our study investigated the relationship between the water
quality and land use in eleven subwatersheds of the NBPR watershed, aiming
to provide land use recommendations to preserve our ecosystems.  The water
quality data were collected monthly from July 2011 to April 2012 and
analyzed for nitrogen, phosphorus, and environmental estrogens (17-beta
estradiol). Additionally benthic macroinvertebrates were investigated in one
subwatershed to test the water quality.  Land use was categorized in terms
of forest cover, agricultural cover, developed areas, and others.  The
correlations were investigated between the land use and water quality.

Results/Conclusions

Our results showed seasonal changes of total phosphate and soluble reactive
phosphate in the eleven streams whereas nitrate concentrations did not have
obvious seasonal change but varied greatly between sites.  The annual
average (July 2011 to April 2012) of total phosphate ranged from 54 to 130
µg/L in different streams and the average of soluble reactive phosphate
varied from 29 to 70 µg/L.  However, nitrate concentrations differ 15 times:
from 0.1 to 1.5 mg/L among streams.  The correlations suggested total
phosphorus decreased with the increased forest cover and it increased with
the increased cover of developed areas as well as impervious cover.  Nitrate
concentrations might be positively related to the agricultural cover.  We
also found environmental estrogens were high in the watershed and closely
associated with rain events: 60-100 pg/mL in base flow and 50-200 pg/mL
after rain events.  In one subwatershed, the benthic invertebrate study
revealed Shannon-Weaver diversity index ranged from 1.0 to 2.3 at five
sites, indicating a relatively healthy ecosystem.  However our watershed
study suggested water quality in the whole watershed should raise concerns,
particularly about phosphate and environmental estrogens.  In order to
improve water quality and ecosystem health of the NBPR watershed, land use
and management ought to be planned appropriately.