Informative Essay about the Water Cycle

Introduction

Among the different definitions of ecosystem services that emerged, the most widely used version is that of the Millennium Ecosystem Assessment (MEA). It defined the term as “the benefits people obtain from ecosystems” (MEA, 2003a, p.53). This definition recognized the interdependence of humans and other species with nature (Costanza et al., 2017). It also identified four types of ecosystem services based on functionality: provisioning, regulating, cultural, and supporting services (MEA, 2003a).

Supporting services are defined as “services necessary for the production of all other ecosystem services.” (MEA, 2003a, p.57). Unlike the other three ecosystem services, humans indirectly use and indirectly feel the impact of supporting services (MEA, 2003a; Costanza et al., 2017). Moreover, supporting services have been considered intermediate services. It has been argued that only final services should be included in environmental valuations to avoid double counting (Martin-Ortega et al., 2015). It can be inferred that these may be some of the reasons why supporting services are one of the lesser-studied ecosystem services as reported in Adhikari and Hartemink's (2016) paper. One example of a supporting service is water cycling.

Water is vital for the survival of life on Earth (Aznar-Sánchez et al., 2019). However, humans have disrupted the natural flow of the water cycle in direct and indirect ways (Bridgewater, Guarino, and Thompson, 2018). Disruption is due to population growth and economic growth which increased demand and consumption of water (De Graaf et al., 2014; Davis et al., 2015). These drivers also led to climate change and land use change which further accelerated water cycling (Davis et al., 2015). The study conducted by Aznar-Sánchez et al. (2019) showed that research on water ecosystem services has grown exponentially from 1998 to 2017 since Costanza et al. (1997) published their work which estimated that the minimum average value of the ecosystem services was US$33 trillion per year. Aznar-Sánchez et al. (2019) also revealed in their study that water research was often associated with agricultural and forestry systems which implies the relevance of water in food production and the provision of other goods and services. Therefore, water cycling, as a supporting ecosystem service, is integral to the functioning of other ecosystem services and entails actions that will maintain the integrity of this service and prevent the further degradation of the environment.

The paper will be discussed as follows: Section II will briefly provide an overview of the water cycle and its importance. This will be followed by Section III which tackles the threats to the water cycle and its implications. Section IV will focus on the actions that can be done to maintain and enhance water cycling.

Background on the water cycle

The water cycle, the movement of water on Earth, has the following major stages: evapotranspiration, sublimation, condensation, precipitation, snowmelt, runoff, streamflow, infiltration, and storage. This process is driven by solar energy. On a global scale, it is a closed system that indicates constant total volume on the planet (Kundzewicz, 2008; USGS, 2016). The residence time of water in shallow and more accessible areas such as soil, wetlands, and lakes is low when compared to ice sheets and glaciers and in larger and deeper water bodies such as groundwater and lakes (Kundzewicz, 2008). The water cycle is responsible for water resource formation, including the creation of water ecosystems (Zhang et al., 2017) that provide other ecosystem services such as habitat and water supply. While around 70% of water is used for agriculture and the rest is divided for industrial, domestic, and municipal use, to name a few, the growth rate for consumption for agricultural purposes is lower than the others (Chen et al., 2016).

The MEA framework depicts that changes in ecosystem services affect human well-being and poverty reduction across time and scale (MEA, 2003b). The following section will focus on the drivers that change the water cycle and its consequences.

Threats to the water cycle and implications

One of the observable changes in the Anthropocene is the disruption in the water cycle (Bridgewater, Guarino, and Thompson, 2018). Several studies have been published providing evidence for the intensification of the water cycle. This includes increased precipitation records in the forest such as the Amazon and northern Pakistan and increased salinity levels such as in the western Atlantic. Climate change, land cover change (Davis et al., 2015), and dam developments (Bosmans et al., 2017) are major causes of the intensification of the water cycle. These factors will most likely change the following fluxes:

a. Climate Change

Climate and water are interlinked. Changes in climatic conditions change the rate of the water cycle. Hence, increased temperature will result in an intensification of the water cycle (Kundzewicz, 2008). Climate change, therefore, is a major threat to this supporting service. The effects of climate change vary depending on the location/area. Wet areas are getting wetter while dry areas are getting drier. Aside from modifications in the frequency and timing of precipitation, more intense rainfall is observed (Capon and Bunn, 2015; Bridgewater, Guarino, and Thompson, 2018). Drought and flooding lead to the destruction of properties, loss of livelihood, and health diseases thereby affecting human well-being.

With higher levels of carbon dioxide in the atmosphere due to increased consumption of fossil fuel, photosynthesis can accelerate which can result in higher water efficiency in plants. However, extreme cases can lead to irreversible damage, especially if such levels are beyond the physiological limits of plants (Antonarakis, 2018). Climate change is also causing sea level rise from the melting of glaciers, ice caps, and ice sheets which results in saltwater intrusion thereby reducing freshwater availability in groundwater reservoirs (Kundzewicz, 2008).

Freshwater ecosystems also have high exposure levels to the effects of climate change due to warming, carbon dioxide enrichment, precipitation, and runoff. Its provisioning services such as food and other raw materials may decrease (Capon and Bunn, 2015). Capon and Bunn attempted to illustrate the effects of climate change on freshwater ecosystems: Fish supply is expected to change in terms of abundance and distribution, while demand may increase if food production from lands becomes difficult due to drier conditions. In terms of freshwater ecosystems' role in climate regulation as a sink for greenhouse gases, climate change may turn these ecosystems into sources of emissions instead. Nutrient cycling may also be affected if the storage capacity of aquatic and riparian soils is altered. Lastly, in terms of cultural services, while some recreational sites may be negatively affected by climate change, there could be a higher demand for other areas less affected (Capon and Bunn, 2015).

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b. Land cover change

[bookmark: OLE_LINK1][bookmark: OLE_LINK2]Historical data revealed that natural vegetation has been converted to croplands, grazing land, and developed areas which again alters the water cycle (Sterling, Ducharne, and Polcher, 2013). According to the study conducted by Sterling, Ducharne, and Polcher (2013), the approximated annual terrestrial evapotranspiration has reduced by 3,500 km3 y-1 (5%) due to land cover change, alongside with 7.6% increase in runoff. However, the authors added that this is counteracted by an increase in evapotranspiration from reservoir creation and irrigation (see Figure 1):

These findings by Sterling, Ducharne, and Polcher (2013) were somehow consistent with the study of Bosmans et al. (2017). Bosmans et al. (2017) argued in their research that land cover change and human water users have the same significant effect in altering the water cycle. Approximately 888 km3 yr-1 or 1.5% of the total evapotranspiration has reduced and increased discharge by 901 km3 yr-1. On the other hand, discharge from human water use was estimated to be 1185 km3 yr-1” (Bosmans et al., 2017).

Around 60-80% of evapotranspiration from land comes from plant transpiration (Schlesinger and Jasechko, 2014). This strengthens the claim that deforestation has significant negative implications for the water cycle. Deforestation loosens the soil which then enhances erosion, surface runoff, flooding, and soil fertility loss (Daily et al., 1997; Schlesinger and Jasechko, 2014). Erosion and runoff lessen the ability of the land to infiltrate water (Daily et al., 1997). Caja et al. (2018) studied the effect of land use change in Angat-Ipo Watershed, the Philippines supplying water to Metro Manila. Land cover change (see Figure 2) was caused by deforestation which resulted in a lower infiltration rate and increased water discharge. Without disregarding changes in precipitation, there was a peak flow change from 391.1 m3 in 2003 to 779.5 m3 in 2010 (Caja et al., 2018).

c. Creation of dams

Increasing water demand has led to water stress and water scarcity to supply water mostly for irrigation, industry, and household use (De Graaf et al., 2014; Sabater et al., 2018). Chen et al. (2016) argued that population has a positive relationship with food consumption and the number of dams constructed. Moreover, data showed a correlation between dam development and economic expansion (Chen et al., 2016). Although dams and reservoirs control the flow of water to prevent floods, generate power, and regulate water supply, one of their major downsides is the alterations in the normal flow which affect habitats, especially the species thriving and dependent on the water bodies. These scenarios have negative effects on biodiversity from which humans benefit. Life cycles are negatively influenced as these species are adapted to the natural changing flows and use them to signal various activities such as feeding and migrating (Lehner et al., 2011). Furthermore, in Sabater et al. (2018) meta-analysis research, there was a benthic algal biomass accumulation increase due to the low water flow. Dams also lead to changes in groundwater recharge and microclimates (Bridgewater, Guarino, and Thompson, 2018). Moreover, there have been recorded incidences of more flooding downstream (Antonarakis, 2018).

As an illustration, the study of Gain and Giupponi (2014) revealed that after the construction of the Farakka Dam, both the minimum and maximum flow in Bangladesh were generally outside the threshold limit which could explain the frequent floods and droughts in the area. There was also an increased salinity level in the river downstream which resulted in fish reduction and mangrove growth constraints. This negatively affected the communities dependent on the ecosystem for their livelihood (Gain and Giupponi, 2014).

Knowing the importance of the water cycle as a supporting service, these drivers of change should be addressed to prevent further negative consequences to the environment and to human well-being.

Actions to maintain/enhance the water cycle

Ecological restoration is a major intervention that can be done to slow down the intensification of the water cycle, and also serve as a mitigation and adaptation measure for climate change. This includes reforestation, watershed management, and wetland conservation and restoration. Reforestation could have different results in different forest ecosystems. It can increase regional temperatures in boreal forests while there can be a temperature decrease in tropical areas (Locatelli et al., 2015). Effects will also vary based on the species planted, especially for high water-use species. This, therefore, calls for careful planning (Locatelli et al., 2015). Restoration is vital, especially in extreme weather events where it can protect communities from run-off and flooding (Locatelli et al., 2015). Soil filtration and groundwater recharge are improved due to reforestation. Moreover, wetland conservation and restoration are essential in flood control, especially vegetated wetlands. Saturated soil increases the chance of runoff. Wetlands are also important ecosystems for groundwater recharge (Maltby and Acreman, 2011). Maltby and Acreman (2011) and Locatelli et al. (2015) argued that the management of these ecosystems depends on a case-to-case basis and no one-fit solution can be replicated in all ecosystems. Through these interventions, not only will it improve the water cycle but it will also deliver other ecosystem services.

Alternation in the natural flow regime due to dams and over-abstraction can be addressed by understanding and controlling environmental flows (e-flows) (Davis et al., 2015) which is described as “the quantity, timing, and quality of freshwater flows and levels necessary to sustain aquatic ecosystems which, in turn, support human cultures, economies, sustainable livelihoods, and well-being” (Arthington et al., 2018, p.4). It will involve a multi-stakeholder approach where users, policymakers, and scientists, among others in the decision-making process (Pahl-Wostl et al., 2013). E-flows could be done by setting limits on river water extraction and use and listing important water bodies such as wetlands (Davis et al., 2015). Several studies have cited the positive environmental, social, and economic impacts of regulating e-flows such as increasing the minimum flow downstream leading to the growth of tree species, increasing water for irrigation, and increasing energy generated for the hydroelectric plant (Foster, Mahoney, and Rood, 2018). With the forecasted increase in dam construction in the future, challenges in implementing e-flows such as resource constraints, lack of information, lack of political will, and support from the public must be addressed to prevent further degradation of aquatic ecosystems (Chen et al., 2016; Arthington et al., 2018).

Improved governance in water ecosystem services across scales (i.e. local, national, regional, global) is imperative. As the water cycle is not constricted in one locality and extends across countries and continents, this only stresses that transboundary cooperation is crucial (Vörösmarty, Hoekstra, and Bunn, 2015). Furthermore, as effective stakeholder engagement is crucial in implementing the e-flows approach, governance will play a critical role in involving people in data collection and monitoring implementation in order to make informed decisions as seen in the case presented by Watts et al. (2018). Climate change calls for adaptive management to ensure strategies are appropriate and still effective (Watts et al., 2018).

Conclusion

Drought, flooding, changes in water quality, water, and food scarcity, and biodiversity loss were among the highlighted consequences of disrupting the water cycle elaborated on in this paper. The major causes identified were climate change, land use change, and the creation of dams. Solutions however are not simply reversing these causes. Ecological restoration tries not only to “decelerate” the water cycle but is also one of the solutions to climate change. Furthermore, although regulating environmental flows could be challenging, especially for developing countries as this will entail data gathering and technical expertise, the benefits will outweigh the costs. Nonetheless, these proposed solutions have demonstrated that enhancing the water cycle as a supporting service improves other ecosystem services. This, therefore, emphasizes the need for collaboration that seeks to maximize the benefits humans derive from the environment.

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