Suitable Land-Use and Land-Cover Allocation Scenarios to Minimize Sediment and Nutrient Loads into Kwan Phayao, Upper Ing Watershed, Thailand

Human activity and land-use changes have affected the water quality of Kwan Phayao, Upper Ing watershed, due to the associated high sediment load and eutrophication. This study aims to identify suitable LULC allocation scenarios for minimizing sediment and nutrient export into the lake. For this purpose, the LULC status and change were first assessed, based on classified LULC data in 2009 and 2019 from Landsat images, using the SVM algorithm. Later, the land requirements of three scenarios between 2020 and 2029 were estimated, based on their characteristics, and applied to predict LULC change using the CLUE-S model. Then, actual LULC data in 2019 and predicted LULC data under three scenarios between 2020 and 2029 were used to estimate sediment and nutrient export using the SDR and NDR models. Finally, the ecosystem service change index identified a suitable LULC allocation for minimizing sediment or/and nutrient export. According to the results, LULC status and change indicated perennial trees and orchards, para rubber, and rangeland increased, while forest land and paddy fields decreased. The land requirements of the three scenarios provided reasonable results, as expected, particularly Scenario II, which adopts linear programming to calculate the land requirements for maximizing ecosystem service values. For sediment and nutrient export estimation under the predicted LULC for the three scenarios, Scenario II led to the lowest yield of sediment and nutrient exports, and provided the lowest average ESCI value among the three scenarios. Thus, the LULC allocation under Scenario II was chosen as suitable for minimizing sediment or/and nutrient export into Kwan Phayao. These results can serve as crucial information to minimize sediment and nutrient loads for land-use planners, land managers, and decision makers.

Biogeochemical and Hydrological Drivers of Heterogeneous Nutrient Exports From Subterranean Estuaries

Submarine groundwater discharge (SGD) to coastal zones contributes terrestrial freshwater and nutrients that may support harmful algal blooms (HABs). The magnitude of nutrient exports via SGD depends on volumes of fresh groundwater discharge, its chemical composition, and modifications by biogeochemical processing within subterranean estuaries. Thus, the ability to upscale SGD exports requires knowing the range of chemical composition of inland groundwater and how those compositions may be transformed as fresh and saltwater mix within subterranean estuaries. These processes may create heterogeneous magnitudes of solute exports, even at small spatial scales, and such heterogeneities have rarely been assessed for regional or global SGD nutrient export estimates. To evaluate heterogeneity in subterranean estuary processes and nutrient export, we collected seasonal pore water samples in 2015–2016 at three proximal (<20 km) subterranean estuary sites in Indian River Lagoon, FL. Sites have homogenous hydrogeological settings, but differ in land use and coastal features, and include a mangrove site, an urban site, and a site offshore of a natural wetland. All sites exhibit little variation through time in nutrient concentrations and modeled SGD rates. In contrast, each site exhibits significantly different nutrient concentrations of potential fresh groundwater sources, fresh groundwater discharge volumes, and nutrient transformations within subterranean estuaries. Groundwater specific discharge correlates with nutrient concentrations, suggesting that higher residence times in the subterranean estuary increase biogeochemical transformations that reduce anthropogenic nutrient loads but increase in situ nutrient sources derived from organic matter remineralization. The differences in transformations lead to SGD nutrient contributions that differ by orders of magnitude between sites and have N:P ratios that are greater than the Redfield ratio (15) for the mangrove (29) and urban sites (28), but less than the Redfield ratio for the wetland site (8). These results indicate that heterogeneity of both absolute and relative nutrient export via SGD complicates integration of nutrient fluxes across regional coastal zones and evaluations of its impacts to coastal ecosystems. A better understanding of the drivers of heterogeneity, including subterranean estuary processes, land use, coastal topography, and vegetation dynamics could improve assessments of regional nutrient loading and upscaling for estimates of global solute cycles.

Effect of Landscape Fragmentation on Soil Quality and Ecosystem Services in Land Use and Landform Types

This study was carried out according to the following objectives in the Shoor River Basin in southwestern Iran: (i) Evaluation of ecosystem services (ES) including habitat quality (HQ), carbon storage (CS), nutrient export (NE), and soil export (SE) using the InVEST approach as well as soil quality (SQ) using an integrated quality index; (ii) Assessment of the relationship between ES and SQ with landscape metrics using Pearson correlation test; and (iii) Investigation of the interaction between ES efficiency, SQ and landscape fragmentation using a ternary plot. The results showed that the northern and eastern parts of the region are prioritized for HQ, CS, and SQ but the southern and western parts for NE and SE. The highest ES efficiency and SQ were found for the forests as well as for the ridge/tops landforms. Statistical analysis clarified that there was a positive and significant relationship between HQ and CS (R>0.8) while the relationship of the two with NE was inverse and significant (-0.55<R<-0.50). The correlation between SE and NE was also positive and significant (R>0.50). SQ was also correlated positively and significantly with HQ and CS (0.43<R<0.5) while no relation with NE and SE was found. It was also perceived that increasing the landscape fragmentation decreases HQ, CS, and SQ but increases NE and SE. Besides, the interaction between ES, SQ, and landscape fragmentation across the sub-basins of the study area can change under the influence of the dominant land use and landform types.

NutSpaFHy—A Distributed Nutrient Balance Model to Predict Nutrient Export from Managed Boreal Headwater Catchments

Responsible forest management requires accounting for adverse environmental effects, such as increased nutrient export to water courses. We constructed a spatially-distributed nutrient balance model NutSpaFHy that extends the hydrological model SpaFHy by introducing a grid-based nutrient balance sub-model and a conceptual solute transport routine to approximate total nitrogen (N) and phosphorus (P) export to streams. NutSpaFHy uses openly-available Multi-Source National Forest Inventory data, soil maps, topographic databases, location of water bodies, and meteorological variables as input, and computes nutrient processes in monthly time-steps. NutSpaFHy contains two calibrated parameters both for N and P, which were optimized against measured N and P concentrations in runoff from twelve forested catchments distributed across Finland. NutSpaFHy was independently tested against six catchments. The model produced realistic nutrient exports. For one catchment, we simulated 25 scenarios, where clear-cuts were located differently with respect to distance to water body, location on mineral or peat soil, and on sites with different fertility. Results indicate that NutSpaFHy can be used to identify current and future nutrient export hot spots, allowing comparison of logging scenarios with variable harvesting area, location and harvest techniques, and to identify acceptable scenarios that preserve the wood supply whilst maintaining acceptable level of nutrient export.

Applying GIS and SWAT to understand the stream network, hydrology, sediment and nutrient export from the Grand River watershed into Lake Erie

Headwater streams are important lotic systems that represent more than 80% of the total stream lengths in watersheds. The dynamic coupling of hydrological and biogeochemical processes in headwaters is responsible for regulating the chemical form, residence time and longitudinal transport of nutrients. Over time, stream modification (e.g. to enhance drainage in agricultural watershed) has altered natural stream flow-paths and thus, stream functionality. Such alteration has resulted in degradation of habitat and water quality, both in upland and downstream waters. Currently, nutrients exported from the Grand River (Ontario) watershed are contributing to eutrophication and Harmful Algal Blooms in Lake Erie. With respect to the Grand River watershed, this thesis examined (1) the impact of agriculture on the existing stream network, (2) the utility of the Soil and Water Assessment Tool to simulate hydrology, sediment and nutrient export that closely correlate with measured data, and (3) the application of Best Management Practices in the watershed with the intent of meeting provincial and transnational nutrient targets. The results showed that compared to the actual ground-truthed stream network, the predicted stream network based on topography underpredicted a total of 2,535 km of actual channel present in the watershed. Channels not anticipated by topography were mostly first-order, with low sinuosity, and were most common in areas with high agricultural land use, and are likely excavated extensions to headwater streams to facilitate drainage. Then, the sediment and nutrient loading at Dunnville, discharging to entering Lake Erie, was predicted to be 2.3[superscript⁻1] 105 t yr[superscript-1] of total suspended sediment, 7.9 [superscript⁻1] 103 t yr-1 of total nitrogen, and 2.5 ⁻1 102 t yr-1 of total phosphorus. Finally, implementing wide buffer strips, stabilizing channel banks and grassed waterways were found to be the most effective practices for reducing sediment and phosphorus loading into Lake Erie.

Applying GIS and SWAT to understand the stream network, hydrology, sediment and nutrient export from the Grand River watershed into Lake Erie

Headwater streams are important lotic systems that represent more than 80% of the total stream lengths in watersheds. The dynamic coupling of hydrological and biogeochemical processes in headwaters is responsible for regulating the chemical form, residence time and longitudinal transport of nutrients. Over time, stream modification (e.g. to enhance drainage in agricultural watershed) has altered natural stream flow-paths and thus, stream functionality. Such alteration has resulted in degradation of habitat and water quality, both in upland and downstream waters. Currently, nutrients exported from the Grand River (Ontario) watershed are contributing to eutrophication and Harmful Algal Blooms in Lake Erie. With respect to the Grand River watershed, this thesis examined (1) the impact of agriculture on the existing stream network, (2) the utility of the Soil and Water Assessment Tool to simulate hydrology, sediment and nutrient export that closely correlate with measured data, and (3) the application of Best Management Practices in the watershed with the intent of meeting provincial and transnational nutrient targets. The results showed that compared to the actual ground-truthed stream network, the predicted stream network based on topography underpredicted a total of 2,535 km of actual channel present in the watershed. Channels not anticipated by topography were mostly first-order, with low sinuosity, and were most common in areas with high agricultural land use, and are likely excavated extensions to headwater streams to facilitate drainage. Then, the sediment and nutrient loading at Dunnville, discharging to entering Lake Erie, was predicted to be 2.3[superscript⁻1] 105 t yr[superscript-1] of total suspended sediment, 7.9 [superscript⁻1] 103 t yr-1 of total nitrogen, and 2.5 ⁻1 102 t yr-1 of total phosphorus. Finally, implementing wide buffer strips, stabilizing channel banks and grassed waterways were found to be the most effective practices for reducing sediment and phosphorus loading into Lake Erie.