The Effect of Sulfate Contamination of Water on Wild Rice Nutrient Composition

Abstract

Sulfate contamination of waters where wild rice grows threatens its survival. Toxic levels of sulfate affect growth and development, which leads to reductions of natural stands. Research shows that when sulfate is reduced to sulfide, it interacts with iron in sediment to precipitate iron-sulfide. Iron-sulfide plaques accumulate on wild rice roots, which inhibits nutrient uptake from soil. This study examined changes in wild rice nutrient composition by analyzing rice samples grown in low-sulfate and high-sulfate waters under natural and experimental conditions. Samples collected from experimental mesocosms included “low-sulfate’ controls (10 mg/L SO4) and “high-sulfate” amended (300 mg/L SO4). Natural site samples collected from two bodies of water surrounding the Great Lakes Region; Big Rice Lake (“low-sulfate” non-detect) and Sand River (“high-sulfate” > 46.2 mg/L SO4), respectively. We measured antioxidant capacity, plant secondary metabolites, total starch, and mineral content, including mercury, of eight wild rice samples. Wild rice exposed to sulfate in natural and controlled environments had decreased seed sizes and weight. Reductions in seed size appeared due to a reduced amount of starch, as starch content and seed size were highly correlated. Certain trace minerals were reduced to a greater degree than the reduction in seed size, particularly iron, copper, and zinc. Since iron and copper are both required for starch synthesis, and copper deficiency increases synthesis of starch-degrading enzymes, deficiencies of copper and iron may be responsible for the reduced starch content of the wild rice seeds, thus producing a smaller seed size.