Riparian Buffer Zones As A Green Technology For Mitigating Surface Runoff Of Pollutants

Introduction

According to a report from WHO, by 2015, approximately 663 million people mostly from developing countries, still consumed untreated water from open surface water bodies such as rivers or streams (WHO, 2015). So, protecting these areas as a potential source for the water consumption or saving aquatic species should be considered (Alemu et al. , 2017). A riparian buffer zone (RBZ) is the interface between land and a river that filters nutrients, sediments and other pollutants from surface runoff before they reach the rivers (Alemu et al. , 2017; Bourgeois et al. , 2016; Chen et al., 2017; Fortier et al. , 2015; Izydorczyk et al. , 2018; Kimura et al. , 2017; Muñoz-Carpena et al. , 2018; Oluju, 2017). It also regulates the river temperature by shading effects of trees in RBZ (Alemu et al. , 2017). These are portions of land that contain thin lines of green vegetation which is strongly influenced by the presence of water and may include flowers, shrubs, trees and grasses (Oluju, 2017). Water-quality benefits are the primary mechanism in RBZ. Vegetation as an important part provides a great resistance to water flow and decline the velocity of surface runoff, so the infiltration of water and deposition of particulates exiting the field area will be increased (Muñoz-Carpena et al. , 2018).

Together, declined surface runoff velocity and increased infiltration can offer water quality improvement benefits. Another mechanism by which RBZ provide water quality improvement is through controlling erosion due to dense, perennial vegetation providing greater resistance to erosion. The eutrophication phenomena in water bodies can also be controlled by RBZs through mitigating the movement of nitrogen (N) and phosphorus (P) as key elements of algal bloom in streams (Fortier et al. , 2015). The remarkable influence of RBZ in the ecosystems is inevitable. When it comes to biodiversity, the RBZ could be home to a variety of organisms, animals and birds (Izydorczyk et al. , 2018). The industrialization and intensive demanding to the agriculture are putting a profound pressure on the remaining RBZs (Izydorczyk et al. , 2018). By 2050, around %20 rise in agricultural land is predicted (Bourgeois et al. , 2016), so remained RBZs are being assumed as an alternative for croplands (Fortier et al. , 2015). It has been asserted, nearly 50 to 80% of buffer zones across Europe and North America have been converted to urban and agricultural lands (Bourgeois et al. , 2016; Boz & Gumiero, 2016).

On the other hand, the intensive animal husbandry is no longer supplied by organic fodder collected from grassy areas of RBZ, thus there is little concern in sustaining the RBZs (Izydorczyk et al. , 2018). Hence, the number of legal regulations and guidelines has been increased toward implementation of buffer zones as a best management practice against pollutant losses from agricultural landscape and helping to sustainable development (Bourgeois et al. , 2016; Izydorczyk et al. , 2018). For instance, in Quebec, the government forbid agricultural practices, pesticides and fertilization applications in the vicinity of rivers with a narrow RBZ (50 years of age) in providing C stocks has been estimated (240 tons/h), around ten times more than a grass buffer zone (Fortier et al. , 2015).

Biodiversity effect

Two main concepts should be considered in RBZs. First, species richness, the number of species present in the area, and the species uniformity which means relative abundance. Therefore, areas that are dominated by a few high-yield species are much less efficient at reducing pollution than areas of the same size but with relatively high species diversity. Species diversity reduces the loss of nitrogen in native, undisturbed grassland soils. Thus, biodiversity is the key to regulating ecosystem function. Within a certain area, plant diversity can alter the abundance of soil microbial communities and control the rate of nitrogen cycling in the ecosystem, thereby regulating the ecosystem (Izydorczyk et al. , 2018).

Controlling Eutrophication Effect

Due to anthropogenic activities, non-point source pollutants particularly nitrogen and phosphorous or both lead to Eutrophication in water bodies. The proliferation of algae, such as Cyanobacteria, can cause a reduction in the total amount of dissolved oxygen in the water and destroys the ecosystem of aquatic organisms by releasing toxic compounds. A successful strategy to address the eutrophication issue is using RBZs in the vicinity of river or lake (Álvarez et al. , 2017).

Sustainability of RBZs

For having sustainable mitigation of pollutants, we can regularly harvest the plants in the RBZ, but it should be collected before the soil is frozen. So, the accumulated nutrients can be removed from the ecosystem effectively. It is not surprising that, if we do not harvest them before winter season, the plants remain in the ecological environment until the winter, and the nutrients accumulated in the plants are converted into soluble forms during the freezing and thawing of the plants. Some of these soluble nutrients may discharge into the aquatic ecosystem through surface runoff.

In nutshell, these areas potentially can be as a rich source of fertilizer or nutrient if we do not have a best management plan for RBZs (Izydorczyk et al. , 2018). Another aspect of sustainability of RBZs is that they can be useful in urban areas by shading buildings with tree cover, reducing cooling costs, minimizing costs associated with repairing problems caused by stormy weather or stream bank erosion.

So, it can support the green economy, create job opportunities and enhances biodiversity. In the United States, most of the green infrastructure is considered urban rainwater treatment systems, such as rain gardens, detention ponds, biological swamps, riverbank wetlands, and green roofs. It is a tool for reducing floods, sewer overflows, and contaminants that spread to other water ecosystems (Mander et al. , 2017).

Conclusion

The study reflected that the RBZs as a green technology meet sustainable development goals (SDG 6, 13,14 and 15) by mitigating surface runoff pollutants, cutting eutrophication, climate change controlling, erosion reduction and supporting the economy in rural and urban areas.