Land-based Loads Research Articles

Habitat suitability modelling to improve understanding of seagrass loss and recovery and to guide decisions in relation to coastal discharge

Habitat suitability modelling was used to test the relationship between coastal discharges and seagrass occurrence based on data from Adelaide (South Australia). Seven variables (benthic light including epiphyte shading, temperature, salinity, substrate, wave exposure, currents and tidal exposure) were simulated using a coupled hydrodynamic-biogeochemical model and interrogated against literature-derived thresholds for nine local seagrass species. Light availability was the most critical driver across the study area but wave exposure played a key role in shallow nearshore areas. Model validation against seagrass mapping data showed 86 % goodness-of-fit. Comparison against later mapping data suggested that modelling could predict ~745 ha of seagrass recovery in areas previously classified as ‘false positives’. These results suggest that habitat suitability modelling is reliable to test scenarios and predict seagrass response to reduction of land-based loads, providing a useful tool to guide (investment) decisions to prevent loss and promote recovery of seagrasses.

Can Forel–Ule Index Act as a Proxy of Water Quality in Temperate Waters? Application of Plume Mapping in Liverpool Bay, UK

The use of ocean colour classification algorithms, linked to water quality gradients, can be a useful tool for mapping river plumes in both tropical and temperate systems. This approach has been applied in operational water quality programs in the Great Barrier Reef to map river plumes and assess trends in marine water composition and ecosystem health during flood periods. In this study, we used the Forel–Ule colour classification algorithm for Sentinel-3 OLCI imagery in an automated process to map monthly, annual and long-term plume movement in the temperate coastal system of Liverpool Bay (UK). We compared monthly river plume extent to the river flow and in situ water quality data between 2017–2020. The results showed a strong positive correlation (Spearman’s rho = 0.68) between the river plume extent and the river flow and a strong link between the FUI defined waterbodies and nutrients, SPM, turbidity and salinity, hence the potential of the Forel–Ule index to act as a proxy for water quality in the temperate Liverpool Bay water. The paper discusses how the Forel–Ule index could be used in operational water quality programs to better understand river plumes and the land-based inputs to the coastal zones in UK waters, drawing parallels with methods that have been developed in the GBR and Citclops project. Overall, this paper provides the first insight into the systematic long-term river plume mapping in UK coastal waters using a fast, cost-effective, and reproducible workflow. The study created a novel water assessment typology based on the common physical, chemical and biological ocean colour properties captured in the Forel–Ule index, which could replace the more traditional eutrophication assessment regions centred around strict geographic and political boundaries. Additionally, the Forel–Ule assessment typology is particularly important since it identifies areas of the greatest impact from the land-based loads into the marine environment, and thus potential risks to vulnerable ecosystems.

Hydro-biogeochemical modeling of the early-stage outbreak of green tide (Ulva prolifera) driven by land-based nutrient loads in the Jiangsu coast

The outbreak of a large-scale green tide (Ulva prolifera) will have a serious impact on marine environment, ecological functions, landscape, and coastal social economy. Eutrophication is generally considered to be the most important driving factor of this phenomenon. It is difficult to obtain the pressure-impact relationship between land-based loading and green tides by only surveying or monitoring, whereas modeling can perform this task easily. In this study, therefore, a hydro-biogeochemical model was established and verified by the measured hydrodynamic and water quality variables. In the initial outbreak area of Jiangsu coast, China, we studied the relationship between U. prolifera bloom and the driving factors of nutrient loads and structures by modeling different scenarios of land source inputs. It was found that the ratio of nitrogen to phosphorus could be affected significantly, which triggered the bloom of U. prolifera. When the land-based input doubled or halved, the dissolved inorganic nitrogen concentration increased 20.6% or decreased 9.5%, respectively, which might result in 14.5% increase or 46.3% decrease in the green tide, respectively. It was also found that the nutrient distribution and structure was affected by the land-based load, which caused the outbreak of U. prolifera. Moreover, the total nutrient load must be controlled to prevent the outbreak of green tide in the Jiangsu coast.

Linking water quality with the total pollutant load control management for nitrogen in Jiaozhou Bay, China

Eutrophication was once the most serious problem for the overload of nitrogen in Jiaozhou Bay, with the development of society and the economy of Qingdao, China. Total pollutant load control management (TPLCM) was applied for 10 years via two five-year plans since 2006 in Qingdao, China, and it was further strengthened after 2011. To evaluate the effect of TPLCM on the water quality of Jiaozhou Bay, dissolved inorganic nitrogen (DIN) was chosen as the water quality factor in response to the land-based load of total dissolved nitrogen (TDN), ammonia nitrogen (NH4-N) and nitrate nitrogen (NO3-N) during 2001–2015. Special attention was given to temporal and spatial changes. The flux of land-based TDN obviously decreased during the period of the ‘11th Five-Year Plan (2001–2010)’ of China, with an approximate 17% annual reduction rate, which caused the annual mean concentration of DIN to significantly decrease in Jiaozhou Bay. The water quality did not significantly improve in the period of the ‘12th Five-Year Plan (2011–2015)’ of China in Jiaozhou Bay. There was little reduction of NO3-N, which was the predominant nitrogen form, although the reduction of NH4-N did occur. The TPLCM in the Dagu River and the Haibo River watershed has occurred since 2000, and it had a considerable reduction in land-based TDN. The seawater quality improved at the northwest and south parts of Jiaozhou Bay. The TPLCM was prompted by insufficient progress in the Lichun River and the Moshui River watershed, and there was continued poor water quality in the north and northeast areas of Jiaozhou Bay from 2001 to 2015. The next phase of the TPLCM should promote land and marine development in a coordinated way, with more attention devoted towards the control of non-point sources, the introduction of advanced sewage treatment and coastal restoration.

Three-dimensional water quality model based on FVCOM for total load control management in Guan River Estuary, Northern Jiangsu Province

Guan River Estuary and adjacent coastal area (GREC) suffer from serious pollution and eutrophicational problems over the recent years. Thus, reducing the land-based load through the national pollutant total load control program and developing hydrodynamic and water quality models that can simulate the complex circulation and water quality kinetics within the system, including longitudinal and lateral variations in nutrient and COD concentrations, is a matter of urgency. In this study, a three-dimensional, hydrodynamic, water quality model was developed in GREC, Northern Jiangsu Province. The complex three-dimensional hydrodynamics of GREC were modeled using the unstructured-grid, finite-volume, free-surface, primitive equation coastal ocean circulation model (FVCOM). The water quality model was adapted from the mesocosm nutrients dynamic model in the south Yellow Sea and considers eight compartments: dissolved inorganic nitrogen, soluble reactive phosphorus (SRP), phytoplankton, zooplankton, detritus, dissolved organic nitrogen (DON), dissolved organic phosphorus (DOP), and chemical oxygen demand. The hydrodynamic and water quality models were calibrated and confirmed for 2012 and 2013. A comparison of the model simulations with extensive dataset shows that the models accurately simulate the longitudinal distribution of the hydrodynamics and water quality. The model can be used for total load control management to improve water quality in this area.

Trends in marine debris along the U.S. Pacific Coast and Hawai’i 1998–2007

We assessed amounts, composition, and trends of marine debris for the U.S. Pacific Coast and Hawai’i using National Marine Debris Monitoring Program data. Hawai’i had the highest debris loads; the North Pacific Coast region had the lowest debris loads. The Southern California Bight region had the highest land-based debris loads. Debris loads decreased over time for all source categories in all regions except for land-based and general-source loads in the North Pacific Coast region, which were unchanged. General-source debris comprised 30–40% of the items in all regions. Larger local populations were associated with higher land-based debris loads across regions; the effect declined at higher population levels. Upwelling affected deposition of ocean-based and general-source debris loads but not land-based loads along the Pacific Coast. LNSO decreased debris loads for both land-based and ocean-based debris but not general-source debris in Hawai’i, a more complex climate-ocean effect than had previously been found.

Improving estimates of oil pollution to the sea from land-based sources

This paper presents improvements to calculation methods used in the National Research Council’s (NRC) Oil in the Sea reports from 2003 and 1985 to estimate land-based contributions of petroleum hydrocarbons to the sea from North America. Using procedures similar to the 2003 report, but with more robust methods for handling non-detections, estimated land-based contributions for 1977 and 2000 were over 50% lower than the best 1996 estimate in the NRC report. The largest loads were from the northeastern United States and the Gulf of Mexico region for both the 2003 report and updated calculations. Calculations involved many sources of uncertainty, including lack of available data, variable methods of measuring and reporting data, and variable methods of reporting values below detection limits. This updated analysis of land-based loads of petroleum hydrocarbons to the sea highlights the continued need for more monitoring and research on inputs, fates and effects of these sources.

A Geographical Analysis of Potential Railway Load Centers in China*

Railway containerization is important to the development of an efficient inland-port distribution (IPD) system in China. After reviewing the general transportation network evolution and local circumstances, a strategy of focusing the limited capital investment at a few railway stations with the highest potential to develop into land-based load centers (LLCs) was proposed. The fifteen major railway stations designated in the 2002 Plan form the basis for an evaluation. With the application of geographic information systems (GIS), each station's potential to become a LLC is evaluated under infrastructural, economic, logistics, and capacity dimensions. The 250- and 500-km hinterland scenarios are considered.

Watershed modelling of nonpoint nitrogen losses from arable land to the Swedish coast in 1985 and 1994

Eutrophication problems in the Baltic Sea have drawn attention to the contribution of nutrients from surrounding countries. By using the HBV-N model in southern Sweden (145 000 km 2) daily nitrogen leaching, reduction in rivers and lakes, net transport to the sea and source apportionment have been calculated in 3725 subbasins for the period 1985–1994, with calibration at 722 sites against measured time series. On average, 48% of the nonpoint losses from agriculture were reduced during the transport towards the sea, which left about 33 500 tonnes in annual mean net transport. This represents 45% of the total land-based load. Land cover and emissions for the years of 1985 and 1994 were used in two separate simulations of the 10-year period. The normalized gross leakage from arable land in 1985 was estimated to 29 kg N ha −1 year −1, which corresponds to 15 kg N ha −1 year −1 in net leakage to the sea. In 1994 these transports were reduced by 20 and 15%, and thereby the total load on the sea was decreased by 7%. This is still far from the Swedish goal of 50% reduction. The article presents the spatial variation of nitrogen leakage and retention within the southern half of Sweden, and emphasizes the importance of allocating measures where down-stream retention is low in order to achieve efficiency with respect to the sea. It is shown that the model approach may be used in the decision making process for best management practices in watersheds.

European land-based pollutant loads to the North Sea: an analysis of the Paris Commission data and review of monitoring strategies

Paris Commission (PARCOM) data have been used to investigate regional patterns in land-based pollutant loads to the southern North Sea for the period 1990–1993. Despite measures to standardise the procedures for obtaining river load estimates, important methodological discrepancies remain. These discrepancies relate to: (i) the location of sampling with respect to tidal and saline limits along the river reach, (ii) frequency of sampling, (iii) whether sampling is periodic or aperiodic and biased to particular flow conditions, and (iv) the choice between two load estimation algorithms. The PARCOM data indicate that riverine and total land-based loads of metals, total-N and total-P to the southern North Sea are dominated by the Rhine/Meuse and Elbe, which have the largest catchment areas and drain major centres of population and industry in central and western Europe. UK rivers have both the highest riverine loads per unit area and the highest direct discharge loads for many determinands. The high loads per unit area may be a function of the relatively small catchment areas and the proximity of major sources of pollution to the downstream monitoring sites. Higher direct discharges for the UK rivers may occur because UK direct discharge estimates include effluent inputs to the freshwater tidal reaches. For the other major European river systems, effluent discharges to the tidal freshwater reaches are included in the riverine load estimate. More thorough evaluation of load estimation methodologies is required if these data are to be used for comparative purposes in an international policy-making and legislative context.