Introduction:
Phosphorus is a vital macronutrient that is frequently restricting
primary production in rivers and lakes. In terms of the Redfield ratio
(106C:16N:1P), even a small addition of P under P-limited conditions
could lead to a significant growth in the primary production of aquatic
ecosystems. This may lead to eutrophication and hypoxia, a water dead
zone, with significant loss of biodiversity and changes in the food web
(Orihel et al., 2017; Dijkstra et al., 2018). As algae may bind
nitrogen, an increase in P-availability may trigger algal outbreaks.
This has been observed in many cases to occur due to excessive
fertilizer and manure applications
For many aquatic systems, soil and particulate-P erosion together with
runoff water are main sources of inputs of P to surface water (Brendel
et al., 2019). Sediment pore water and desorption from its solid phase
replenish P in overlying waters, and become available for consumption by
aquatic organisms. It has long been acknowledged that soil and sediment
bound P is only partly biologically available to plants and aquatic
organisms as algae (Van Rotterdam et al., 2012). The bioavailable
fraction of P can be evaluated by algal bioassays (Liu et al., 2016).
Although algal assays are difficult to conduct and time-consuming, the
bioavailable P estimated by assays is considered well to quantify the
potential of sediment P to cause eutrophication (Young et al., 1985;
Ekholm and Krogerus, 2003). Indeed, the quantification of bioavailable
phosphorus for algal growth was shown to be essential to estimate
eutrophication risks (Ellison and Brett, 2006; Okubo et al., 2012).
However, it is attractive to predict bioavailable P using a chemical
measure that is simple, routinely applicable, and cost-efficient. A
single chemical extraction that allows to screen a large number of
samples and monitor the health of aquatic ecosystems requires that the
relationship between bioavailability of P from algal bioassay
experiments and chemically extracted P is clear and unambiguous.
A great deal of chemical extraction approaches have been evolved to
estimate bioavailable P roughly in soil and sediments such as those
developed by Morgan (1954), Mehlich (1983), Bray-Kurtz (1961), Colwell
(1952) and Olsen et al. (1954). Chemical extractants are based on
different mechanisms and abilities to extract P and may diverge from the
chemical used for extraction as well as e.g. sediment: water ratio,
equilibration (shaking) time, and targeted P pools. For instance Bray-P
may be useful for acid, but not for calcareous materials. Also Mehlich-P
is based on extraction by acid, but performs better for high pH soils.
Olsen-P extracts with NaHCO3 and is more commonly used
for pH-values exceeding slightly acid values, as it was developed for
alkaline soils. The well-known 0.1 M NaOH extractant is one of first
methods developed to quantify algal available P (Young, 1982). Anderson
and Magdoff (2005) reported that Olsen-P had the highest correlation
with Selenastrum capricornutum growth in comparison with other
extractants. Huettl et al, (1979) suspended sediments with
hydroxy-aluminum modified cation exchange resin and detected that the P
adsorbed onto resin had good magnitude of agreement withSelenastrum capricornutum (r2 = 0.98; n = 5).
The well-known 0.01M CaCl2-extraction (Boekhold et al.,
1993) provided excellent results for agricultural soils that are
regularly limed. Sharpley (1993) used a selective extraction that was
based on establishing contact between a soil suspension and Fe-oxide
coated paper strips that were developed by Van Der Zee et al. (1987).
The so-called Fe-oxide paper strips significantly estimated bioavailable
P from runoff sediment for P-deficient Selenastrum capricornutum(Sharpley, 1993).
Rivers are the main components of Urmia Lake ecosystems and flow in
circuitous path from cities, agricultural lands, industrial area, etc.,
and then end up in Urmia saline lake. They are also perceived as
delivering nutrient to the Lake and wetlands around it by biogeochemical
processes. However, eutrophication processes are becoming dominant
wetlands degradation around the Lake (Arfania et al., 2018), which is a
prominent habitat of migrant birds. Soil degradation is gradually
becoming the main obstacle to provide ecosystem services for
irresistible Urmia Lake basin. Therefore, to develop phosphorus
management and deal effectively with adverse legacy effects of
sedimentary phosphorus, we investigate bioavailability of P for the
aquatic ecosystem. To verify our argument this study was conduct to 1)
develop P bioavailability assessment in sediments according to several
single chemical extractions and with P-inhibited algal growth, and 2)
recognize influencing factors in P management in sustaining aquatic life
and deteriorate sediment ecosystem service.