While multiple sources of nutrients attributable to algae blooms exist, primarily nitrogen and phosphorus, low water flows and temperature do not necessarily lead to algae blooms unless adequate nutrients are present to drive rapid growth of algae (Herald, Aug. 15).
Given the location of the abundant algae growth in the Animas River, the source of nutrients is more likely municipal wastewater rather than fertilizers applied mainly to grass pastures and hay fields along the river.
Fertilizers reaching the river must move by surface flow and/or subsurface lateral flow. During the summer growing season when evapotranspiration is high in our region, subsurface lateral flow should not be a source of nutrients unless soil water below the root zone becomes saturated, an unlikely scenario particularly for sprinkler-irrigated fields. Surface runoff of water from sprinkler-irrigated fields would be minimal.
The section of the Animas currently affected by the algae bloom has only a few grass fields adjacent to the river; most are located on the mesa to the east above the river.
Vegetation and wetland area plants adjacent to the river can capture nutrients for their growth that might be derived from surface and subsurface water flows from agricultural fields.
Consequently, to say fertilizers are contributing to the current localized algae bloom is misleading; the most likely nutrient source is the direct discharge of Durango’s municipal wastewater to the Animas River.
Charles MacKown
Durango
