James M. Bishop

Generally unseen and infrequently measured, submarine groundwater discharge (SGD) can transport potentially large loads of nutrients and other land-based contaminants to coastal ecosystems. To examine this linkage we employed algal bioassays, benthic community analysis, and geochemical methods to examine water quality and community parameters of nearshore reefs adjacent to a variety of potential, land-based nutrient sources on Maui. Three common reef algae, Acanthophora spicifera, Hypnea musciformis, and Ulva spp. were collected and/or deployed at six locations with SGD. Algal tissue nitrogen (N) parameters (δ15N, N %, and C:N) were compared with nutrient and δ15N-nitrate values of coastal groundwater and nearshore surface water at all locations. Benthic community composition was estimated for ten 10-m transects per location. Reefs adjacent to sugarcane farms had the greatest abundance of macroalgae, low species diversity, and the highest concentrations of N in algal tissues, coastal groundwater, and marine surface waters compared to locations with low anthropogenic impact. Based on δ15N values of algal tissues, we estimate ca. 0.31 km2 of Kahului Bay is impacted by effluent injected underground at the Kahului Wastewater Reclamation Facility (WRF); this region is barren of corals and almost entirely dominated by colonial zoanthids. Significant correlations among parameters of algal tissue N with adjacent surface and coastal groundwater N indicate that these bioassays provided a useful measure of nutrient source and loading. A conceptual model that uses Ulva spp. tissue δ15N and N % to identify potential N source(s) and relative N loading is proposed for Hawai'i. These results indicate that SGD can be a significant transport pathway for land-based nutrients with important biogeochemical and ecological implications in tropical, oceanic islands.

Study focus: We investigated connections between land uses and submarine groundwater discharge (SGD) nutrient fluxes to coastal waters of Maui, Hawai'i. Nutrient contributions from agricultural lands, wastewater injection, and septic-cesspool systems were examined by combining a numerical groundwater model with 18 O H 2 O , 15 N NO 3 -, and 18 O NO 3 -modeling to identify groundwater pathways, recharge elevations, and nitrate sources. Fresh and total SGD rates and nutrient fluxes were quantified using 222 Rn mass balance modeling. New hydrological insights for the region: Low nitrate + nitrite (N + N) SGD fluxes (24 mols/d) were measured where groundwater flowed beneath primarily undeveloped land on transit to the coast. By contrast, of all land use types, sugarcane and pineapple fields contributed the largest amount of N to coastal waters via SGD (3800 mols/d). Despite their much smaller freshwater flux, these SGD sources provide substantially larger N fluxes than the State's largest rivers (avg. 700 mols/d). Septic systems, cesspools, and near coast wastewater injection wells also contribute N + N to groundwater and coastal waters, although in much smaller quantities. This study demonstrates that numerical groundwater modeling combined with geochemical modeling can be used to determine sources and flux of nutrients in SGD and provides a unique, original, and practical framework for studying the effect of land use and its impact on nutrient delivery to coastal waters.

This paper summarizes the results of a study, which was conducted during the period of 1996-2005. It assesses the impact of river diversion (Third River), marsh drainage, and marsh restoration on Kuwait's marine environment. The results indicated lower salinity, higher nitrate concentration, higher chlorophyll-a, and higher sedimentation in the northern waters of Kuwait influenced by the discharge of the man-made Third River and marsh drainage. Five estuarine copepod species, which occur only in the northern waters of Kuwait due to their proximity to the mouth of the river, are reported here for the first time. Lower turbidity levels were observed in the northern waters of Kuwait during 2004 and 2005 possibly influenced by the marsh restoration process. The above results indicate the close interrelationship between the upstream river environment and the northern Arabian Gulf. River-related activities in the Tigris-Euphrates Basin have transboundary impacts downstream. Assumptions on the potential effects of the upstream damming of the Tigris and Euphrates Rivers on Kuwait's marine environment are included. It is expected that recent and planned river basin modifications in Turkey, Iran and Iraq will significantly reduce river discharge, permanently remove seasonal flooding, and impact the northern Gulf's marine environment, with serious implications for fisheries.