What are the reasons for a significant negative correlation among heavy metals such as Cadmium (Cd) and Lead (Pb) with fecal coliform, BOD, NO3, and PO4 during the wet period?
According to Gafur et.al. (2018) The concentrations of As, Hg, and Pb
in water, samples were identified by inductively coupled plasma mass spectroscopy (ICP–MS), while concentrations in sediment samples were determined by particle-induced X-ray emission (PIXE). Results showed that the concentrations of As, Hg, and Pb in water ranged from 66 to 82,500 g/L, 17 to 2080 g/L, and 11 to 1670 g/L, respectively. These levels exceeded, by 1000 to 10,000 times, the safe limits of drinking water defined by the World Health Organization, which indicated that Bone River water is not safe for drinking or cooking purposes.
doi:10.3390/w10111507
NO3 and phosphorus are been used in fertilizers and some heavy metals act as catalysts for producing them So small amount of metals come through fertilizers and maybe cause contamination. The correlation matrix helps to verify the source of the contamination and its dependence.
Thank you for your answers. The main point of my question is about the reasons for a significant negative correlation, for instance, between Pb and fecal coliform?
River basin dramatically increased waters of the were highly polluted by Mn, Co, Cu, Zn, Mo, Cd, and Pb.
Could be it related to a different origin?:
Fecal coliform and nutrients come, mostly, from domestic wastes, while the metals you mentioned (Cd, Pb) are related to industrial wastes.
If so, the relationship between their concentrations must be weak or negative.
I am not finding the graphs of the data to show the nature of the "negative" correlation but:
1. Metals will tend toward the bottom of the water body, eventually, I expect, being precipitated by putrefaction reaction byproducts and becoming part of the bottom accumulations.
2. Fecal Coliforms are living. Given a protected environment, nutrients, like phosphorous and nitrates, the population of these is likely to vary great deal depending on sampling location and time of day.
I would not expect these (fecal coliforms) concentrations to be related, at all, to heavy metals concentrations given that the sources are mostly unrelated. Fish farms, untreated human waste, can spike BOD5. Industrial waste, and given your metals composition, natural runoff and/or mining/construction might be expected to be contributors - those metals are often difficult to define their source. Se might be a good, additional marker. I am probably missing it but the database, showing sample quality (numbers for given metrics) and location of sample, including depth, would maybe help clarify their respective significance. I expect these have been reviewed but, just in case, might be helpful:
Article Assessment of the characteristic of nutrients, total metals,...
https://www.usgs.gov/mission-areas/water-resources/science/linking-selenium-sources-ecosystems-irrigation?qt-science_center_objects=0#qt-science_center_objects
María Soledad Rodriguez Alvarez Thank you for this suggestion. It is completely true that the best way of finding our answers is by studying and reviewing the literature.
Negative correlation quite possible in wet season because of dilution process.
I agree with Virendra that it might be related to the season/hydrological conditions. In the Netherlands, during rain events phosphate and nitrate are flushed from the top layers of the soil, a quick route towards the surface water. During drying periods, the surface water is supplied by groundwater to a greater extend, and that may contain higher elemental (e.g. metal) concentrations due to mineral dissolution (without any particular source of contamination present).
The concentration of heavy elements increases depending on the polluted source being released to the water bodies as well as depends on the size of the surface and what is added from the water sources. The most impact is the high temperature that moves the heavy elements within the food chain due to the increase in biological activities
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