9.5.3 Types of Riparian Vegetation and Their Pollutant
Removal Capacity
There are two most prominent types of vegetation studied in the riparian ecotone,
viz. grasses and forest, with their type varying from region to region. The two
predominant vegetation types have different roles in the pollutant removal. The
grass riparian ecotones are capable of filtering sediments and pollutants associated
with sediments such as phosphorus and nitrogen (Parkyn 2004). Further there are
reports that grass riparian ecotones are less effective in the removal of soluble
nutrients such as nitrate, ammonia and dissolved phosphorus and nitrate removal
is greater in forested buffers compared to grasses (Parkyn 2004).
The role of riparian buffer strips in relation to nitrogen has been well studied
(Peterjohn and Correll 1984; Daniels and Gilliam 1996). There is a large variability
in the removal efficiency of N ranging from 20 to 100% (Valkama et al. 2019). The
removal of N and P via vegetation in the riparian ecotone varies widely, and it is
difficult to predict (Hoffmann et al. 2009) as the hydrological regimes controlling the
biogeochemical processes in the riparian zone change along the river continuum
(Hoffmann et al. 2009). None of the riparian ecotone vegetation types, viz. grass or
forested, are much effective in reducing concentration of dissolved phosphorus
(Parkyn 2004). In most of the research monitoring, the effectiveness of buffer
zones for their pollutant removal capacity has focused on vegetated filter strips
(VFS) (Parkyn 2004).
Riparian forest reduces the nitrate input into the river via the uptake by plant roots
(Silvan et al. 2002; Palviainen et al. 2004), retention to soil and utilisation by the
microbes (Silvan et al. 2002; Palviainen et al. 2004), also via gaseous N fluxes from
soil to the atmosphere (Silvan et al. 2002). The different fractions of nitrogen, viz.
ammonium, nitrate and dissolved organic nitrogen, undergo transformation in the
soil for their effective utilisation and assimilation. The riparian forest decreases the
concentration of ammonium and dissolved organic nitrogen in surface runoff more
than nitrate (Kokkonen et al. 2006).
During the 1980s and 1990s, the mechanism of phosphorus removal by riparian
buffers has been studied by several researchers. The mechanisms explained are
deposition of phosphorus attached with sediment, settling of particulate phosphorus
and adsorption of dissolved phosphorus by clay particles in particular clay
containing high levels of aluminium and iron (Reddy et al. 1999). Further there
are reports of phosphorus reduction via uptake from understory vegetation and
microorganisms (Silvan et al. 2004).
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S. Sharma et al.
Removal Capacity
There are two most prominent types of vegetation studied in the riparian ecotone,
viz. grasses and forest, with their type varying from region to region. The two
predominant vegetation types have different roles in the pollutant removal. The
grass riparian ecotones are capable of filtering sediments and pollutants associated
with sediments such as phosphorus and nitrogen (Parkyn 2004). Further there are
reports that grass riparian ecotones are less effective in the removal of soluble
nutrients such as nitrate, ammonia and dissolved phosphorus and nitrate removal
is greater in forested buffers compared to grasses (Parkyn 2004).
The role of riparian buffer strips in relation to nitrogen has been well studied
(Peterjohn and Correll 1984; Daniels and Gilliam 1996). There is a large variability
in the removal efficiency of N ranging from 20 to 100% (Valkama et al. 2019). The
removal of N and P via vegetation in the riparian ecotone varies widely, and it is
difficult to predict (Hoffmann et al. 2009) as the hydrological regimes controlling the
biogeochemical processes in the riparian zone change along the river continuum
(Hoffmann et al. 2009). None of the riparian ecotone vegetation types, viz. grass or
forested, are much effective in reducing concentration of dissolved phosphorus
(Parkyn 2004). In most of the research monitoring, the effectiveness of buffer
zones for their pollutant removal capacity has focused on vegetated filter strips
(VFS) (Parkyn 2004).
Riparian forest reduces the nitrate input into the river via the uptake by plant roots
(Silvan et al. 2002; Palviainen et al. 2004), retention to soil and utilisation by the
microbes (Silvan et al. 2002; Palviainen et al. 2004), also via gaseous N fluxes from
soil to the atmosphere (Silvan et al. 2002). The different fractions of nitrogen, viz.
ammonium, nitrate and dissolved organic nitrogen, undergo transformation in the
soil for their effective utilisation and assimilation. The riparian forest decreases the
concentration of ammonium and dissolved organic nitrogen in surface runoff more
than nitrate (Kokkonen et al. 2006).
During the 1980s and 1990s, the mechanism of phosphorus removal by riparian
buffers has been studied by several researchers. The mechanisms explained are
deposition of phosphorus attached with sediment, settling of particulate phosphorus
and adsorption of dissolved phosphorus by clay particles in particular clay
containing high levels of aluminium and iron (Reddy et al. 1999). Further there
are reports of phosphorus reduction via uptake from understory vegetation and
microorganisms (Silvan et al. 2004).
212
S. Sharma et al.