Effects of road salt on fish assemblages in Maryland

Road salt usage ensures safe winter driving conditions on high traffic volume highways such as the federal interstate system and state primary and secondary roads.  However, there are often excessive and repetitive applications of road salt, depending on storm severity and frequency.  I used the Maryland Biological Stream Survey (MBSS) data base to examine water quality collected during the MBSS Spring Index period and fish assemblage data from the MBSS Summer Index period for Maryland.  Statistical analyses indicated that there are significant changes in fish assemblages in first, second and third order streams, with simpler assemblages (two – three tolerant fish species) present in streams with very high chloride levels.  The number of intolerant fish species declines significantly at chloride levels greater than 100 mg/L, along with decreases in fish assemblage diversity and the Maryland Fish Index of Biotic Integrity.  Stream chloride levels during the MBSS spring index often exceed 150 mg/l, and may underestimate actual winter levels.  Although multiple road-related stressors are often present, road salt is an important stressor to fish assemblages, and needs to be considered in conservation of intolerant Maryland fish species and stream biodiversity.