Many arid-land rivers are naturally nutrient-limited.  In the middle Rio Grande in central New Mexico, nutrient sources are primarily related to wastewater effluent and irrigation practices.  Nutrient limitation and other environmental parameters can affect primary producers.  We studied relationships among periphyton biomass, species assemblages and environmental parameters in the middle Rio Grande.  Quarterly longitudinal river surveys and nutrient-diffusing substrate experiments have examined effects of nitrogen and phosphorus levels, as well as turbidity and pH, on periphyton parameters (chlorophyll a, species assemblages). Higher nutrient levels in the lower reaches are related to upstream wastewater effluent inputs and may influence periphyton biomass.  Additionally, increased turbidity is a major factor in shaping algal community, creating a light-limited environment where primary productivity is limited to a littoral zone “bathtub ring.”  Higher turbidity limited periphyton biomass with chlorophyll a ranging from 15-20 mg L^-1 at upstream sites but only 1-2 mg L^-1 at more turbid downstream sites.  Preliminary data indicate periphyton communities are more diverse in upstream sites where turbidity is lower and substrates more diverse.  Understanding the diversity and drivers of periphyton dynamics in arid-land rivers are crucial to our understanding of how management in the middle Rio Grande watershed affects this riverine ecosystem.