Seasonal Inundation Research Articles

Sargassum brown tide impacts nearshore water quality and seagrasses in Jobos Bay, Puerto Rico

The Caribbean region is experiencing seasonal inundation of the shoreline by large mats of pelagic Sargassum spp. (Sargassum) leading to novel impacts to ecological communities. Where Sargassum becomes trapped along the shoreline, leachates turn the water a brown color, coined Sargassum Brown Tide (Sbt). We conducted monthly sampling at six sites along the offshore mangrove keys of Jobos Bay, PR between April 2022 to July 2023 to collect temperature, pH, salinity, dissolved oxygen, total nitrogen (TN), total phosphorus (TP), chlorophyll a (chl a), total suspended solids (TSS), and volatile suspended solids (VSS) at nearshore, midshore, and offshore zones along transects running perpendicular to the shoreline. We also collected data on submerged aquatic vegetation (SAV) community dynamics along transects at each site. We found significantly higher chl a and lower dissolved oxygen concentrations within the nearshore zone during Sbt events but the differences did not extend out to the midshore and offshore zones. Total suspended solids were also higher at nearshore zones compared to offshore zones when a Sbt event occurred. In addition, sites that experienced Sbt had higher turbidity and lower pH. Total percent cover of SAV was different between sites impacted by Sbt and control sites depending on transect zone, with higher SAV percent cover for control sites within the 5 m zone and often within the 15 m zone. Our data suggest that Sbt has significant impacts to nearshore water quality, chl a, and SAV percent cover; however, most impacts are not seen beyond 45 m in well flushed systems.

Mississippi River-floodplain connectivity level mediates fish assemblage dynamics

The life histories of many Louisiana fishes are tied to the timing, magnitude, and duration of the Mississippi River flood pulse. Anthropogenic modifications designed to control and restrict flood waters have decoupled Louisiana’s floodplains from the seasonal flood pulse, influencing the aquatic food web. Culvert and rock weir repair within the Richard K. Yancey Wildlife Management Area aims to improve water quality and maintain appropriate water depth for native Louisiana fishes. In this study we conducted high-resolution imaging sonar (ARIS Explorer 3000) monitoring of the floodplain fish assemblage across seasons prior to hydrologic restoration. Imaging sonars may be used to obtain quantitative ecological and behavioral information without the selectivity biases of traditional techniques through the recording of continuous video-like datasets that are not constrained by environmental factors such as turbidity. Our first objective was to test the hypothesis that seasonal inundation levels and proximity to the Mississippi River affect the abundance and size class distribution of the floodplain-associated fish assemblage. Our second objective was to characterize species composition and ecological function of each acoustically-detected size class using historical fisheries datasets collected by the Louisiana Department of Wildlife and Fisheries. To do so, we employed the multi-gear mean standardization technique for standardizing catch per unit effort of passive and active gear types used within the historical dataset in order to produce a non-exhaustive list of potentially recorded species by the imaging sonar. Our study demonstrated a size class dependent use of floodplain habitats mediated by inundation level, but not the distance from the Mississippi River. Our results illustrated a trend of increased detections of all size classes during high-water connected-spring and summer periods, as well as during disconnected-summer periods immediately following the seasonal flood pulse. Continued monitoring of the fish assemblage will provide additional data to better describe the complex dynamic patterns the floodplain fish assemblage may exhibit in response to the seasonal flood pulse and hydrologic restoration efforts.

Exploration of large-scale vegetation transition in wet ecosystems: a comparison of conifer seedling abundance across burned vs. unburned forest-peatland ecotones in Western Patagonia

Altered fire regimes, combined with a warmer and drier climate, have been eroding the resilience of temperate rainforests and peatlands worldwide and leading to alternative post-fire vegetation communities. Chronic anthropogenic burning of temperate rainforests at the forest-peatland ecotone in western Patagonia appears to have shifted vegetation communities in poorly-drained sites from forests dominated by the threatened conifer, Pilgerodendron uviferum, to peat-accumulating wetlands covered by Sphagnum mosses. We collected and modeled post-reburn field data using ordinations and hierarchical Bayesian regressions to examine mechanisms through which P. uviferum forests may recover following fire or become locked into alternative development pathways by comparing biophysical factors of a reburned ecotone to those of an unburned (control) ecotone. We found that, (1) the significantly higher densities of P. uviferum trees and seedlings in the forested patches at both the reburned and control sites were associated with significantly lower seasonal water tables, lower cover of Sphagnum mosses and higher cover of other mosses (i.e., not in the Sphagnum or Dicranaloma genera); (2) despite abrupt boundaries in vegetation at both sites, successive fires homogenized the environment at the reburned site; and (3) the distinct life forms and individual species that characterized the understory plant communities across the ecotones affected seedling abundance by shaping microtopography and the substrates available for establishment. Together, our results suggest that fire can push edaphically wet P. uviferum-dominated sites towards a non-forested state by reducing the diversity of microsite structure and composition, thereby placing P. uviferum seedlings in direct competition with Sphagnum mosses and potentially limiting the availability of microsites that are protected from both seasonal inundation and seasonal drought. If wildfires continue under increasingly warmer and drier conditions, the forest-peatland ecotone of western Patagonia may be susceptible to large-scale transformation towards a non-forested state.

Unravelling groundwater budget in the Poyang floodplain system under intensifying seasonal lake inundation

Unravelling groundwater budget in the Poyang floodplain system under intensifying seasonal lake inundation

Influence of anti-seasonal inundation on geochemical processes of arsenic speciation in the water-level-fluctuation zone soil of the Three Gorges Reservoir, China

Influence of anti-seasonal inundation on geochemical processes of arsenic speciation in the water-level-fluctuation zone soil of the Three Gorges Reservoir, China

Inner Niger Delta Inundation Extent (2010–2022) Based on Landsat Imagery and the Google Earth Engine

The Inner Niger Delta (IND), one of the largest floodplain systems in Africa, sustains the livelihoods of more than three million people and is a driver of the rural economy of Mali as far as agriculture, fish production, and livestock are concerned. Because the IND ecosystem and economy are flood-dependent, it is important to monitor seasonal flooding variations. Many attempts to accomplish this task have relied on detailed datasets, such as daily discharge, daily rainfall, and evapotranspiration, which are not easily accessible for data-sparse areas. Additionally, because the area is large, this remains a challenging task. In this study, the interannual variability of seasonal inundation in the IND was investigated by leveraging the computing power of the Google Earth Engine and its large catalogue of open datasets. The main objective was to analyse the temporal and spatial distributions of the inundation extent during the last 13 years. A collection of Landsat 5, 7, 8, and 9 images were composited and different bands were used with various water and vegetation indices in a pixel-based supervised classification to detect the flood extent between 2010 and 2022. A significant improvement in classification accuracy was observed thanks to the different indices. The results suggest a general increasing trend in the maximum annual inundation extent. Throughout the study period, the maximum inundated area varied between 15,209 km2 in autumn 2011 and 21,536 km2 in autumn 2022. The upstream water intake led to a decrease of about 6–10% of the inundated area. Similar fluctuations in the inundated area, precipitation, and river discharge were observed. The proposed approach demonstrates a great potential for monitoring annual inundation, especially for large areas such as the IND, where in situ measurements are sparse.

Study of Alternative Inundation Management Based on Water Conservation in Sub Drainage System of Parung River, Kediri City

Parung River drainage sub system is located in Kediri City. At the peak of the rainy season inundation often occurs on hos cokroaminoto road, kilisuci road and terusan kaliombo road, the cause is reduced water catchment areas and drainage capacity can’t accommodate discharge, so it is necessary to handle water conservation-based inundation. The analysis conducted was modelling the sub-system using the Storm Water Management Model (SWMM) version 5.1 with a 5-year return period. Rainfall calculation used 10 years of daily rain data (2012-2021) from 3 rain stations (Mrican, UPT Kediri, and Pesantren). The 5-year return period results is 129.4 mm/day, then the intensity of rain is calculated using the Mononobe formula. To calibrate the model, comparing observation discharge with simulated discharge of SWMM resulted the Nash-Sutcliffe efficiency number is 0.62 and the correlation R is 0.91. The results of the existing simulation show that Parung River drainage sub-system was not able to accommodate the 5-year return period discharge, impacting 27 overflow points. Water conservation based handling with the application of infiltration wells and rainwater harvesting can reduce discharge on land ranging from 51.58% to 90.91%, while in the channel successfully reduces discharge from 1.73% to 90.40%.

Mapping small inland wetlands in the South-Kivu province by integrating optical and SAR data with statistical models for accurate distribution assessment

There are several techniques for mapping wetlands. In this study, we examined four statistical models to assess the potential distribution of wetlands in the South-Kivu province by combining optical and SAR images. The approach involved integrating topographic, hydrological, and vegetation indices into the four most used classifiers, namely Artificial Neural Network (ANN), Random Forest (RF), Boosted Regression Tree (BRT), and Maximum Entropy (MaxEnt). A wetland distribution map was generated and classified into 'wetland' and 'non-wetland.' The results showed variations in predictions among the different models. RF exhibited the most accurate predictions, achieving an overall classification accuracy of 95.67% and AUC and TSS values of 82.4%. Integrating SAR data improved accuracy and precision, particularly for mapping small inland wetlands. Our estimations indicate that wetlands cover approximately 13.5% (898,690 ha) of the entire province. BRT estimated wetland areas to be ~ 16% (1,106,080 ha), while ANN estimated ~ 14% (967,820 ha), MaxEnt ~ 15% (1,036,950 ha), and RF approximately ~ 10% (691,300 ha). The distribution of these areas varied across different territories, with higher values observed in Mwenga, Shabunda, and Fizi. Many of these areas are permanently flooded, while others experience seasonal inundation. Through digitization, the delineation process revealed variations in wetland areas, ranging from tens to thousands of hectares. The geographical distribution of wetlands generated in this study will serve as an essential reference for future investigations and pave the way for further research on characterizing and categorizing these areas.

Taxonomic and functional structure of understorey bird assemblages on Amazonian seasonally flooded river islands

Abstract The seasonal inundation of the floodplains of the Amazonian rivers is a natural and strong environmental filter for biota. Its effects on the taxonomic and functional attributes of assemblages, however, remain poorly understood. We investigated the taxonomic and trait diversity of understorey bird assemblages on fluvial islands subject to dramatic seasonal flooding in the Amazon. Birds were captured using mist-nets on ten fluvial islands and at 17 sites in unflooded terra firme forests. We captured 1552 individuals of 116 bird species in 4144 net-hours. Average capture rates were similar between the forest types, but species diversity was higher in terra firme forests. The bird assemblages of the islands showed higher species dominance, with only three species accounting for 47% of the individuals captured. Functional space was occupied similarly in both bird assemblages, as indicated by functional dispersion indices (Fdis). In contrast, functional evenness (Feve) was lower in the river island assemblages indicating that the dominant species share similar traits. Functional divergence indices (Fdiv) showed substantial niche differentiation between the bird assemblages of the two forest types. Low inter-annual variability in avian taxonomic and trait diversity was observed in river islands, probably associated with the predictability of the flooding regime.

Monitoring and Analyzing the Seasonal Wetland Inundation Dynamics in the Everglades from 2002 to 2021 Using Google Earth Engine

Inundation dynamics coupled with seasonal information is critical to study the wetland environment. Analyses based on remotely sensed data are the most effective means to monitor and investigate wetland inundation dynamics. For the first time, this study deployed an automated thresholding method to quantify and compare the annual inundation characteristics in dry and wet seasons in the Everglades, using Landsat imagery in Google Earth Engine (GEE). This research presents the long-term time series maps from 2002 to 2021, with a comprehensive spatiotemporal depiction of inundation. In this paper, we bridged the research gap of space-time analysis for multi-season inundation dynamics, which is urgently needed for the Everglades wetland. Within a GIS-based framework, we integrated statistical models, such as Mann–Kendall and Sen’s Slope tests, to track the evolutionary trend of seasonal inundation dynamics. The spatiotemporal analyses highlight the significant differences in wet and dry seasons through time and space. The stationary or permanent inundation is more likely to be distributed along the coastal regions (Gulf of Mexico and Florida Bay) of the Everglades, presenting a warning regarding their vulnerability to sea level rise.

Free and underfit-scavenger river dynamics dominate the large Amazonian Pacaya-Samiria wetland structure

The Peruvian Amazon is known for harboring the greatest biodiversity on the planet, with a world record for biodiversity per unit area. Previous studies suggested that the high ecological value depends on correlations between ecosystem functionality and seasonal inundation control vegetation patches. However, the knowledge on how river morphodynamics and its complex erosion-depositional processes influence the aquatic mosaic and fishing activity in the region is still incipient. This study examines the hydrogeomorphology of the Peruvian tropical wetland of Pacaya Samiria, located in Western Amazonia, and its role in the distribution of aquatic habitats. By using remote sensing techniques, the hydrogeomorphological connectivity that bounds the Pacaya Samiria National Reserve is characterized by ancient to modern river processes. Additionally, river signatures developed by the Ucayali, Marañon, Huallaga, Pacaya, and Samiria Rivers overlap with fish extraction and dominant vegetation to describe how geomorphology is associated with the spatial distribution of fishing zones. Results indicated that paleochannels regulate wetland drainage within the Ucamara Depression, supporting stational water stagnation, vegetation cover, and formation of carbon rich detritus, relevant aspects to understand fish traits. Moreover, the Ucayali River dominates river dynamics in the Pacaya Samiria wetland, thus playing a pivotal role in shaping the complexity of streams and lakes. Furthermore, underfit-scavenger meandering rivers are observed in areas where paleochannels from large rivers are found. A geomorphological characterization of drainage patterns in freshwater environments, such as Amazonian wetlands, is crucial to develop sound management strategies. This methodological approach is expected to support decision-making in conservation actions in Amazonian environments based on understanding wetland connectivity and hydrogeomorphological behavior and their influence on commercial fisheries.

Seasonal flooding decreases fruit-feeding butterfly species dominance and increases spatial turnover in floodplain forests of central Amazonia.

The seasonal flood pulse in Amazonia can be considered a primary driver of community structure in floodplain environments. Although this natural periodic disturbance is part of the landscape dynamics, the seasonal inundation presents a considerable challenge to organisms that inhabit floodplain forests. The present study investigated the effect of seasonal flooding on fruit-feeding butterfly assemblages in different forest types and strata in central Amazonia. We sampled fruit-feeding butterflies in the canopy and the understory using baited traps in adjacent upland (unflooded forests-terra firme), white and blackwater floodplain forests (várzea and igapó, respectively) during the low- and high-water seasons. Butterfly abundance decreased in the high-water season, especially of dominant species in várzea, but the number of species was similar between seasons in the three forest types. Species composition differed between strata in all forest types. However, the flood pulse only affected butterfly assemblages in várzea forest. The β-diversity components also differed only in várzea. Species replacement (turnover) dominated the spatial β-diversity in igapó and terra firme in both seasons and várzea in the high-water season. Nonetheless, nestedness was relatively higher in várzea forests during the low-water season, mainly due to the effect of dominant species. These results emphasize the importance of seasonal flooding to structure butterfly assemblages in floodplain forests and reveal the idiosyncrasy of butterfly community responses to flooding in different forest types. Our results also suggest that any major and rapid changes to the hydrological regime could severely affect floodplain communities adapted to this natural seasonal hydrological cycle, threatening the existence of these unique environments.

Temporal changes in limno-morphometric characteristics in a floodplain lake within Cross River ecosystem during low water period

Iyieke Lake is one of the floodplain lakes within the middle reaches of the Cross River, it is a major foraging and breeding site of several fish species. It is not directly connected to any river, so the water level depends on seasonal inundation by the Cross River. With gradual changes in precipitation and consequent alteration in flooding pattern, and increased agricultural activities around the lake, there are indications of steady annual decline in water level and quality, and lake area. In order to understand the effect of these changes on the aquatic biota, the morphology and some limnological parameters of the lake were studied during low water period (March-May) in 2005, 2011 and 2019 at interval of 6.5 years. Water samples were collected from the lake and the limno-morphological parameters measured at the littoral and limnetic zones of the lake following standard procedures. The results showed that monthly rainfall was significantly (p<0.05) lower in 2019 compared to 2005 and 2011, while minimum and maximum temperature trended conversely (p<0.05). The mean total dissolved solids (TDS) increased from 13.00mg/l in 2005 to 39.33mg/l in 2019 and conductivity trended the same. Mean nitrate (0.92mg/l) and phosphate (1.78mg/l) were higher in 2019 compared to 2005 and 2011. Contrarily, transparency decreased from 0.45m in 2005 to 0.19m in 2019. Similarly, mean dissolved oxygen (3.80mg/l), maximum length (443.20m) and width (314.50m) declined significantly toward 2019 (p<0.05). Lake length, transparency, conductivity and TDS that were seemingly good predictors of water deterioration could be useful in modelling, which is vital in conserving the biodiversity of the Cross River floodplain ecosystem.

Physiological and ecological characteristics and reproductive responses of Phragmites australis to dry-wet conditions in inland saline marshes of Northeast China.

Inland saline marshes in northeastern China have unique soil characteristics and population distribution features. Hydrological change is a critical environmental factor causing wetland degradation and soil salinization in this region. The growth and reproductive responses of typical wetland plants to dry-wet alternations are essential for restoring inland saline marshes. A pot experiment was conducted to study the growth and reproductive responses of Phragmites australis populations to three hydrological treatments simulating drought degradation (drought), permanent inundation restoration (flooding), and seasonal inundation restoration (dry-wet). The species showed different growth and reproductive responses to the three treatments. After 120 d, the drought conditions induced a lower biomass, root length and root surface area of P. australis, but with higher root diameter, soluble sugar, and Na+ ion contents. Flooding and alternating dry-wet treatments induced the opposite responses. Alternating dry-wet treatments can be considered a better solution to effectively conserve water and meet the water needs of P. australis in the current growing season. The biomass under the alternating wet and dry treatment was the same as that under flooding, but the number of rhizome shoots was lower. The alternating dry-wet treatments was able to recover the growth of P. australis in the current season, but the potential for asexual reproduction of the species was insufficient.

A coastal population of Honey Badger Mellivora capensis at Chilika Lagoon in the Indian east coast

We report the presence of the Honey Badger Mellivora capensis from Chilika lagoon, state of Odisha, on the Indian East coast for the first time. Despite being catholic in its habitat choice, it is mainly associated with more arid landscapes comprising savanna, shrubland and desert. Chilika is a coastal lagoon drained by river Mahanadi, and, is situated in the Northern Deccan Plateau ecoregion, which is characterized by dry deciduous forests situated in the rain shadow of the Eastern Ghats mountain range. Chilika is mainly a wet landscape with many portions experiencing seasonal inundation. The lagoon probably gives refuge to an extension of the Eastern Ghats Honey Badger population.

Groundwater dynamics of a lake-floodplain system: Role of groundwater flux in lake water storage subject to seasonal inundation

Groundwater dynamics of a lake-floodplain system: Role of groundwater flux in lake water storage subject to seasonal inundation

Spatiotemporal diet shifting in a neotropical fish species: The role of riparian vegetation and seasonal inundation

Aquatic organisms that consume resources from riparian vegetation or floodplain forests act as trophic links between aquatic and terrestrial ecosystems. For instance, the pacu Piaractus mesopotamicus (Holmberg 1887), which is a migratory fish species, can play an important role in this interaction on Neotropical floodplains. We compared the stomach content of individuals from this species between two different parts of a large river floodplain during contrasting hydrological seasons to quantify the spatiotemporal contribution of allochthonous and autochthonous resources in their diet. Moreover, we performed a bipartite network approach to evaluate the sensitivity of these populations to a simulated loss of food resources through the potential deforestation of riparian vegetation. We found that in the upper catchment, individuals fed mainly on allochthonous items, but their identity depended on the season: fruits were the most abundant resource during the wet season, whereas leaves were more consumed during the dry season. In the lower catchment, the contribution of allochthonous resources was slightly lower in the dry season than in the wet season, when the pacu was able to explore the floodplain. Finally, the results from our consumer-resource network model indicated that this system is vulnerable to riparian deforestation since P. mesopotamicus is highly dependent on input from the riparian vegetation items to its feed.

Characteristics and Sources of DOM in Lake Sediments Under Different Inundation Environments

The characteristics and sources of DOM in sediments are significantly affected by fluctuations in lake water levels. However, the impact of spatial differences on water levels remain unclear. Here, 36 sediment samples were collected from the flood passage and coastal beach of East Dongting Lake. The differences in the composition and source of DOM in sediments under perennial inundation and seasonal inundation were studied using UV-visible absorbance (UV-Vis) and fluorescent excitation-emission matrix (EEM)-parallel factor analysis (PARAFAC). Three fluorescent components of DOM in the sediment were identified. The relative abundance of protein-like components was as high as (72.95±8.94)%, including tryptophan (C2) and tyrosine (C3). However, the humic-like component (C1) abundance was (27.05±8.94)%. Compared with that in perennial inundation, DOM in seasonal inundation had a higher and lower relative abundance of protein-like components and humic-like components, respectively. Further, the aromatic and hydrophobic components were higher in perennial inundation, showing a spatial pattern of the middle>entrance>outlet of the lake, which was more conducive to the migration of pollutants. The high FI (1.93) and BIX (0.91) and low HIX (1.57) indicated that the DOM in sediments had the mixed characteristics of being mainly endogenic and relatively weakly terrigenous. This was mainly influenced by human input and sediment characteristics. The direct effect of sewage discharge was intensified by sediment exposure in the seasonal inundation zone. Additionally, the contents of clay and total nitrogen (TN) were significantly positively correlated with FI, indicating that high nutrients and clay in sediments enhanced the endogenous input of DOM (FI>1.9). The perennial inundation zone was influenced by external runoff input. At the same time, the pH and C/N were significantly positively correlated with HIX and C1, indicating that DOM in the sediments had higher terrigenic characteristics (HIX=1.38±0.57) than those in the seasonal inundation zone owing to the alkaline environment (pH>7.5) and runoff input. The results above revealed the relevant theories of the response of DOM in sediment to water quality and pollution in the process of hydrology and human activities and provide a scientific basis for the prevention and control of sediment pollution in lakes.

Seasonal inundation dynamics and water balance of the Mara Wetland, Tanzania based on multi-temporal Sentinel-2 image classification

Anthropogenic hydrologic alternations are a threat to flood dependent wetland ecosystems like The Mara Wetland in Tanzania, which plays an important role in regulating the quality, timing and magnitude of the flow of water into Lake Victoria and provides natural resources and habitat for a variety of species. Baseline information on the spatiotemporal dynamics of the seasonal inundation is critical to manage potential threats such as dam construction and local climate change, but is challenging to acquire due to the heterogeneity of the landscape caused by the interspersion of open water and emergent vegetation. In this study, intra- and inter-annual inundation pattern of the Mara Wetland are reproduced for 2017–2019 using remotely sensed data. A Random Forest (RF) algorithm is trained bi-seasonally, using eight Sentinel-2 bands, five water- and vegetation-indices and a Digital Surface Model (DSM) to classify the land cover of the wetland region in a semi-automated way, by processing a total of 73 Sentinel-2 scenes based on wet- and dry-state training images for 2017. The scenes are classified into seven classes; three wetland- and four dryland-classes. The overall classification accuracy achieved (based on an independent validation set) is 98.6%. The inundation extents are used in combination with available hydrological field-data to estimate the water balance. The seasonal expansion and contraction of the wetland follows a consistent bi-modal regime, and the results from the water balance affirm the importance of river-flow during the dry-season and local precipitation for the seasonal fluctuations in water-availability.

Seasonality of inundation in geographically isolated wetlands across the United States

Inundation area is a major control on the ecosystem services provisioned by geographically isolated wetlands. Despite its importance, there has not been any comprehensive study to map out the seasonal inundation characteristics of geographically isolated wetlands over the continental United States (CONUS). This study fills the aforementioned gap by evaluating the seasonality or the long-term intra-annual variations of wetland inundation in ten wetlandscapes across the CONUS. We also assess the consistency of these intra-annual variations. Finally, we evaluate the extent to which the seasonality can be explained based on widely available hydrologic fluxes. Our findings highlight significant intra-annual variations of inundation within most wetlandscapes, with a standard deviation of the long-term averaged monthly inundation area ranging from 15% to 151% of its mean across the wetlandscapes. Stark differences in inundation seasonality are observed between snow-affected vs. rain-fed wetlandscapes. The former usually shows the maximum monthly inundation in April following spring snowmelt (SM), while the latter experiences the maximum in February. Although the magnitude of inundation fraction has changed over time in several wetlandscapes, the seasonality of these wetlands shows remarkable constancy. Overall, commonly available regional hydrologic fluxes (e.g. rainfall, SM, and evapotranspiration) are found to be able to explain the inundation seasonality at wetlandscape scale with determination coefficients greater than 0.57 in 7 out of 10 wetlandscapes. Our methodology and presented results may be used to map inundation seasonality and consequently account for its impact on wetland functions.