**6. Conclusion**

Eutrophication is a major problem in the marine ecosystems that is driven primarily by N and P loading. Nitrogen and P pollution are contributed from both point and non-point sources. Many countries have been successful at controlling point sources for both N and P, however non-point sources remains a major problem. Phosphorus input into freshwater and subsequently marine systems are a result of anthropogenic activities that result in excess P with agricultural fertilizers serving as the leading cause of excess P. Historically, reactive N was contributed primarily by microorganisms and microbial activity. In recent years, reactive N is contributed by a myriad of anthropogenic activities which are led by fertilizer and manure application and fossil fuel inputs. While P is transported to the marine ecosystem in particulate and dissolved form, N is translocated as particulate, dissolved and gaseous form. The volatility and mobility of N makes it difficult to control and manage. In marine ecosystem, the salinity condition favors availability of P while limiting planktonic N fixation. This indicates that translocated N has greater effect on marine ecosystem than onsite fixed N. The consequence of N and P loading in freshwater and marine systems is multifaceted with eutrophication perhaps having the greatest impact. Eutrophication can result in increased incidence and significance of algae bloom, anoxic conditions, ocean acidification, and altered plant species diversity. The effects of eutrophication are production of toxins that affect human and animal health, fish kills that negatively impact the food security, food web disruption, and dead zones that disrupt ecosystem functioning. Further, the disruptions in ecosystem functions translate to negative impacts to the tourism industry with economic consequences. Therefore, eutrophication mitigation is essential in order to prevent excessive N and P loading to lotic and lentic systems from upslope anthropogenic activities and subsequently reaches marine ecosystems. The previous literature and investigations

indicate that mitigation strategies should focus on both N and P loading reduction to ensure sustainability. Mitigation strategies to reduce the impact of N & P loading include reduction of leaching from agricultural activities, growing perennial plants, prudent application of fertilizers, and planting winter cover crops to reduce nutrient leaching via increased plant uptake. Strategies include policy and/or industry standard modifications that are likely more controversial yet likely the key to sustainable practices. These strategies include reduction of fossil fuel N emissions through transportation demand reductions, vehicle efficiency advancements, enhanced removal of NOx from exhaust, and stricter emission standards for the transportation system. Further, terrestrial and aquatic ecosystem restoration in terms of flora and fauna are critical to ensure greater quantities N and P are effectively trapped or tied up prior to reaching marine ecosystems. Overall, measures to control eutrophication need to focus on dual nutrient reduction, instead of focusing on N or P alone in order to ensure sustainability, unless there is evidence that focusing on only one nutrient is justifiable for a given ecosystem.
