Water-stained leaves: formation and application as a field indicator of wetland hydrology

Wetland delineations conducted in the United States utilize field indicators as proxy measures of the presence or absence of wetland hydrology. Water-stained leaves provide a practical, qualitative field indicator of wetland hydrology; however, the formation of water-stained leaves has not been elucidated. In response, leaves from six tree species were examined under five treatments to investigate the water-staining process and concomitant timeframes. Results indicate that leaf staining occurred within 14-21 days of continuous exposure to wetland waters and sediment under both laboratory and field conditions. Leaf staining was characterized by readily observable shifts in leaf color (i.e., decreasing Munsell hue, value, and chroma) causing the leaves to appear very dark or black. No color shifts associated with leaf staining occurred in treatments exposed to upland conditions. The timeframe associated with leaf staining corresponds with established wetland hydrology criteria requiring a minimum hydroperiod of 14 consecutive days of soil saturation, flooding, or ponding. Leaves exposed to wetland waters and sediment underwent color shifts significantly faster and to a greater extent than leaves inundated with deionized water, likely as a result of increased microbial abundance and the presence of anaerobic conditions in the simulated wetland treatments. Results suggest that water-stained leaves 1) are a useful and reliable wetland hydrology field indicator for wetland delineation purposes, 2) may provide a proxy measure of wetland hydroperiod, and 3) Munsell color measurements can help differentiate between leaves exposed to wetland and upland conditions.

A New Conceptual Framework for Integrating Earth Observation in Large-scale Wetland Management in East Africa

Wetlands are abundant across the African continent and provide a range of ecosystem services on different scales but are threatened by overuse and degradation. It is essential that national governments enable and ensure the sustainable use of wetland resources to maintain these services in the long run. As informed management decisions require reliable, up-to-date, and large coverage spatial data, we propose a modular Earth observation-based framework for the geo-localisation and characterization of wetlands in East Africa. In this study, we identify four major challenges in spatial data supported wetland management and present a framework to address them. We then apply the framework comprising Wetland Delineation, Surface Water Occurrence, Land Use/Land Cover classification and Wetland Use Intensity for the whole of Rwanda and evaluate the ability of these layers to meet the identified challenges. The layers’ spatial and temporal characteristics make them combinable and the information content, of each layer alone as well as in combination, renders them useful for different wetland management contexts.

A Deterministic Topographic Wetland Index Based on LiDAR-Derived DEM for Delineating Open-Water Wetlands

Wetlands play a significant role in flood mitigation. Remote sensing technologies as an efficient and accurate approach have been widely applied to delineate wetlands. Supervised classification is conventionally applied for remote sensing technologies to improve the wetland delineation accuracy. However, performing supervised classification requires preparing the training data, which is also considered time-consuming and prone to human mistakes. This paper presents a deterministic topographic wetland index to delineate wetland inundation areas without performing supervised classification. The classic methods such as Normalized Difference Vegetation Index, Normalized Difference Water Index, and Topographic Wetness Index were chosen to compare with the proposed deterministic topographic method on wetland delineation accuracy. The ground truth sample points validated by Google satellite imageries from four different years were used for the assessment of the delineation overall accuracy. The results show that the proposed deterministic topographic wetland index has the highest overall accuracy (98.90%) and Kappa coefficient (0.641) among the selected approaches in this study. The findings of this paper will provide an alternative approach for delineating wetlands rapidly by using solely the LiDAR-derived Digital Elevation Model.

A Tidal Flat Wetlands Delineation and Classification Method for High-Resolution Imagery

As an important part of coastal wetlands, tidal flat wetlands provide various significant ecological functions. Due to offshore pollution and unreasonable utilization, tidal flats have been increasingly threatened and degraded. Therefore, it is necessary to protect and restore this important wetland by monitoring its distribution. Considering the multiple sizes of research objects, remote sensing images with high resolutions have unique resolution advantages to support the extraction of tidal flat wetlands for subsequent monitoring. The purpose of this study is to propose and evaluate a tidal flat wetland delineation and classification method from high-resolution images. First, remote sensing features and geographical buffers are used to establish a decision tree for initial classification. Next, a natural shoreline prediction algorithm is designed to refine the range of the tidal flat wetland. Then, a range and standard deviation descriptor is constructed to extract the rock marine shore, a category of tidal flat wetlands. A geographical analysis method is considered to distinguish the other two categories of tidal flat wetlands. Finally, a tidal correction strategy is introduced to regulate the borderline of tidal flat wetlands to conform to the actual situation. The performance of each step was evaluated, and the results of the proposed method were compared with existing available methods. The results show that the overall accuracy of the proposed method mostly exceeded 92% (all higher than 88%). Due to the integration and the performance superiority compared to existing available methods, the proposed method is applicable in practice and has already been applied during the construction project of Hengqin Island in China.

TOWARD A MULTI-SOURCE REMOTE SENSING WETLAND INVENTORY OF THE USA: PRELIMINARY RESULTS ON WETLAND INVENTORY OF MINNESOTA

Wetlands are highly productive ecosystems that offer unique services on regional and global scales including nutrient assimilation, carbon reduction, geochemical cycling, and water storage. In recent years, however, they are being lost or exploited as croplands due to natural or man-made stressors (1.4 percent in 5 years within the USA). This decline in the extent of wetlands began legislative activity at a national scale that mandate the regulate use of wetlands. As such, the need for cost-effective, robust, and semi-automated techniques for wetland preservation is ever-increasing in the current era. In this study, we developed a workflow for wetland inventorying on a state-wide scale using optimal incorporation of dual-polarimetry Sentinel-1, multi-spectral Sentinel-2 and dual polarimetry ALOS-PALSAR with the Random Forest (RF) classifier in Google Earth Engine (GEE). A total of 45 features from a stack of multi-season/multi-year SAR and Optical imagery (included more than 5000 imagery) was extracted over Minnesota state, USA. We followed the Cowardin classification scheme for clustering the field data. The classification was performed in two levels in 5 different ecozones that cover the Minnesota state. Depending on the availability field data for each ecozone overall accuracies changed from 77% to 85%. The variable importance analysis suggests that Sentinel-2 spectral features are dominant in terms of their capability for wetland delineation. Sentinel-1 backscattering coefficient was also superior among other SAR features. Ultimately, the results of this study shall illustrate the applicability of free of charge earth observation data coupled with the advanced machine learning techniques that are available in GEE for better restoration and management of wetlands.

Opportunistic wetland formation, characterization, and quantification on landforms reclaimed to upland ecosites in the Athabasca Oil Sands Region

Surface mine operators in the Athabasca Oil Sands Region (AOSR) of northeastern Alberta are required by regulation to mitigate habitat impacts resulting from their operations, including impacts to wetlands. To date, most land reclamation efforts have focused on recreating upland forestlands that resemble the surrounding natural (dry) boreal forest. However, the surficial conditions on these reclaimed upland sites can also promote spontaneous wetland development. At Suncor’s Base Plant mine, opportunistic wetlands occurring on reclamation sites have not been formally included in the current inventory of reclaimed wetland areas and remain largely unquantified. We characterized and delineated an estimated 210 ha of opportunistic wetlands (consisting of shallow open water, marshes, and swamps) using aerial photo interpretation and remote sensing analysis in combination with follow-up field verifications. The remote-based (desktop) delineations consistently underestimated actual wetland extents, due mainly to underestimations in the extent of non-inundated vegetation zones (e.g., wet meadow) as well as shrubby swamp. After field corrections, opportunistic wetland habitat was estimated to constitute ~ 17% of the total study area (1209 ha), representing more than a fourfold increase in aerial wetland extent associated with reclaimed landforms over that delineated prior to this study. The interspersion of opportunistic wetlands with upland reclaimed landforms, although unintended, more closely reflects the pre-disturbance landscape, which was characterized by a matrix of forestlands, peatlands, and mineral wetlands (in contrast to the more peatland-dominated lowlands). At Suncor, wetland vegetation composition varied significantly across the study area and was influenced by topographic variation (e.g., in elevation and % slope) in combination with the reclamation substrates (soils) that were placed prior to seeding/planting. Thus, the inclusion of opportunistic wetland delineation in reclamation tracking and closure planning merits consideration as does the opportunity to manipulate current reclamation practices to promote the establishment and persistence of wetlands on reclaimed landforms.

Evaluating the use of iron-coated tubes for wetland delineation in South Africa: A pilot study in the Kruger National Park

The identification of hydric soils is important for wetland delineation and protection. South Africa currently uses the Department of Water Affairs and Forestry (DWAF) wetland delineation guidelines which can be subjective in certain contexts. A robust technical standard that can be legally conclusive is therefore required and should be developed for South African conditions. The National Technical Committee of Hydric Soils (NTCHS, 2007) in the United States of America has accepted the Indicator of Reduction in Soils (IRIS) tube methodology as a technical standard, but this had not yet been tested in South Africa. It is proposed that the NTCHS (2007) be adapted for use in South Africa. These Fe-coated tubes are installed into the soil and if reducing conditions are present, the Fe coating is removed. The aim of this study was to evaluate the use of IRIS tubes as a technical standard for wetland delineation in South Africa. The study took place in three different wetland systems (Malahlapanga, Nshawu and the Tshuthsi spruit) in the Kruger National Park. Piezometers were installed in triplicate in each zone, and the water table, pH and Eh were recorded monthly. Soils were classified, soil wetness indicators identified, and vegetation described. The study took place from September 2012 to August 2013. The areal percentage of paint removed from the top 300 mm of the IRIS tubes was quantified by scanning the tubes and then compared to the DWAF wetland indicators. It was found that the DWAF indicators and the IRIS tube method were mostly in agreement; however, the conditions at the Tshutshi spruit were not favourable for Fe reduction, and hence the use of IRIS tubes, due to the high pH values recorded. The IRIS tubes were therefore a useful tool for wetland delineation in the majority of conditions, but are not recommended in high pH, sodic environments. Further research is recommended over a wider geographical area as well as testing the MIRIS methodology (Manganese Indicators of Reduction in Soils) in wetlands that would inhibit Fe reduction.