The role of surface and groundwater inputs in driving water quality in Kāneʻohe Bay, Oʻahu
Recent findings suggest that in the Indo-Pacific region total submarine groundwater discharge (SGD) is estimated to be 3 to 4 times greater than riverine freshwater fluxes and that in the Pacific, large islands alone are responsible for at least 50% of fresh groundwater input. Kāneʻohe Bay located on Oʻahu is a semi-enclosed embayment with seven perennial streams and significant nutrient load as well as algal overgrowth problems. While streams have been investigated as sources of nutrients, SGD here has never been quantified. Our preliminary findings suggest that in wet periods surface runoff dominates terrestrial freshwater fluxes. Groundwater flow, though, responds to the same precipitation increase with a few month’s delay, yet with a peak extending months beyond the end of the wet season. The overall goal of the proposed project is to identify groundwater outcrop locations and quantify SGD and SGD-derived nutrient inputs in Kāneʻohe Bay. In addition, we propose to examine the hydrological regime shift between fresh SGD versus stream dominance during wet/dry seasonal cycles. The final products of this project will include SGD distribution maps, long-term SGD and nutrient flux records, and total stream discharge estimates. We will produce the first comprehensive estimate of terrestrial water input in Kāneʻohe Bay, identify locations of SGD inputs that may potentially be sources of pollutants and nutrients, and determine the extent of groundwater plumes within the bay.
Watch a podcast on this project here.