Ecosystem Threats

Over the past decade some progress has been made in protecting the long-term biological integrity of the Darby Creeks. However, as agricultural and urban development pressures continue to increase, there is an increase in associated stresses to the system. Stresses to the Darby ecosystem connected with agriculture and urban sources are many and varied.

Aerial view of farm fields © TNCSediment, nutrient and chemical loading from agricultural fields and the stormwater runoff from urbanizing areas

represent the primary threats from a water quality perspective. Land use in the drainage basin has historically been production agriculture, with approximately 80% of the land area in fields row-cropped in a corn-soybean rotation.

However, because Columbus is now one of the fastest growing cities in America, conversion of the watershed from agricultural to urban land uses

presents an increased threat to the health of this aquatic system.

Large intense pulses of water entering both the tributaries and mainstems of the Darby Creeks are the result of stormwater runoff and subsurface

drainage systems. Such pulses can result in downstream flooding, the destabilization of stream banks, and the disruption of both streambed and riparian habitats.

Stresses to the Darby Aquatic System

Agricultural Runoff

Presently, sedimentation is the major stress to the Darby system. Sediment threatens the streams’ populations of fresh water mollusks by restricting

their ability to filter the microscopic organisms on which they feed. As these sediments are deposited on the riverbed, they cover the sandy-gravel habitat of many fish and invertebrate species, shielding food sources, reducing spawning sites and suffocating eggs and larvae. Water clouded with sediment during spawning season may disrupt reproduction, as members of some fish species are unable to find one another to mate.

Currently the primary source of sedimentation is from conventional tillage agriculture. However, as suburbanization increases, sedimentation from

construction and stream destabilization will become more important and may surpass agriculture as the major cause of sedimentation in the Darbys.

Nutrient enrichment threatens oxygen sensitive aquatic species. Nutrient enrichment is caused by organic wastes from farm animals, nitrogen and

phosphorus runoff from agricultural and lawncare fertilizers, septic system effluent and urban stormwater runoff. These nutrients enrich water for algae growth in much the same manner that they enrich soil for the growth of row crops. Respiration and subsequent decay of excessive algal biomass often results in subsequent oxygen depletion, negatively impacting those species that require relatively high oxygen levels.

Urban Growth

Chemical contamination can impact aquatic organisms in a variety of ways. High levels of toxic pollutants such as agri-chemicals, septic effluent,

lawncare chemicals, chlorine, and other types of hazardous wastes can result in the direct mortality of a variety of pollution intolerant organisms, especially those species which are relatively immobile (i.e. mollusks). Chemical contamination is caused by agriculture, lawncare, sewage treatment facilities, industrial discharges, and stormwater runoff.

Removal of riparian vegetation raises the temperature of stream water, often beyond the tolerance of adapted species. The aquatic communities in

the Darby have adapted over time to certain environmental parameters, including a specific range of water temperature needed to sustain their life processes. The Darbys are warm water habitats. Stream water temperature is affected by the amount of solar radiation reaching the water surface, and the temperature of tributary waters. Impervious surfaces such as roofs and pavement absorb heat from sunlight, and thus runoff from such surfaces can also contribute heat to streams, as does discharge from industrial sites, treatment plants, septic systems and combined graywater/stormwater flows.

Habitat DestructionDirect physical alteration of the stream channel alters critical habitat components and the flow dynamics of the stream. Habitat

fragmentation, and in some instances, destruction, represent a stress to the species and natural communities of the Darby watershed. The wooded riparian corridor now has gaps in its once continuous canopy. Agricultural conversion and residential development continue to take away the natural corridor of trees and grasses native to the Darbys. Cattle with unrestricted access to stream channels and riparian areas are a source of degradation of habitat quality.