Abstract

Primary production during the growing season in the low-gradient meadow streams of the Valles Caldera in northern New Mexico (USA) is dominated by submerged aquatic macrophytes. A catastrophic wildfire beginning on June 28, 2011, the Las Conchas fire, burned 36% of the East Fork Jemez River catchment above an intensively instrumented stream reach where water quality, hydrology, and aquatic ecology are being studied. Submerged macrophyte biomass in the late summer of 2011 was reduced about 20% after a series of high turbidity spates (>1200 NTU) in late July through early September. Stable flows and deposition of fire-related nutrient-rich sediments in the fall of 2011 led to maximum mean macrophyte biomass during the three-year period of study of 234 g ash free dry-mass (AFDM) m⁻² in October of 2011. Peak mean biomass in 2012 was 228 g AFDM m⁻² in September, during a growing season with only minor hydrologic and water quality disruptions. A major regional storm over multiple days in mid-September of 2013 produced the highest discharge during the three years of study with turbidities reaching ∼400 NTU. Peak mean biomass in 2013 did not reach levels measured in 2011 and 2012. Elodea canadensis was more sensitive to biomass removal during these high flow conditions while Ranunculus aquatilis added biomass following higher flow conditions in 2011 and 2013. Disturbance impacts on submerged macrophytes from major wildfires can be both negative and positive depending upon species types, stream hydrology, catchment geomorphology and water quality.

Highlights

• Catastrophic forest fire disturbed streams dominated by submerged macrophytes.
• Monsoonal floods and a large regional flood reduced standing mean plant biomass.
• Post-fire flooding created a fertilization effect that increased macrophyte biomass.
• Total mean plant biomass ranged from 42 to 234 g AFDM m⁻² over the study period.
• Macrophyte species responses to floods and fertilization events varied between taxa.

Citation

Thompson V.F., Marshall D.L., Reale J.K., Dahm C.N. (2019): The effects of a catastrophic forest fire on the biomass of submerged stream macrophytes. Aquatic Botany 152: 36-42. DOI: 10.1016/j.aquabot.2018.09.001

This Paper/Book acknowledges NSF CZO grant support.