The changes in water sample quality are driven by both natural factors (ecological and natural regulation) and human factors (the current main cause). Different water samples need to be precisely collected through water samplers to assist in determining the causes of the changes. The specific details are as follows:
1. Natural factors: Relying on physical, chemical and biological actions
Hydro-meteorology: Heavy rain washes away surface pollutants, causing an increase in water turbidity, nitrogen and phosphorus levels. Water samplers are needed to collect runoff samples for monitoring indicators. The rise in water temperature promotes the reproduction of algae (prone to algal blooms), and strong winds stir up sediment to release heavy metals. Water samplers are needed to collect water samples from the bottom layer to investigate secondary pollution.
Geology and geomorphology: The water hardness in the limestone area is high (scaling when boiling water), and the water in the sulfide mining area is acidified and has a high iron content. Groundwater replenished through polluted areas will retain pollutants. Water samplers are needed to collect water samples from different depths to test the mineralization degree and VOCs.
Biological activities: The reproduction of algae releases algal toxins, the excrement of aquatic organisms increases organic matter, and the decomposition of bacteria consumes oxygen, causing black and odorous water bodies. Water samplers are needed to collect surface water samples to monitor algal toxins and DO (dissolved oxygen).
2. Human factors: Disrupting the natural balance of water bodies
Domestic pollution: The direct discharge of domestic sewage increases COD and ammonia nitrogen (the main cause of black and odorous urban rivers), and the leaching of domestic garbage releases heavy metals. Water samplers are needed to collect water samples from sewage outlets to trace the source of pollution.
Industrial pollution: Chemical and electroplating wastewater is discharged in violation of regulations, containing heavy metals, strong acids and strong alkalis. Industrial solid waste leachates and pollutes water bodies. Water samplers are needed to collect water samples from the discharge outlet and downstream to accurately detect the concentration of pollutants.
Agricultural pollution: The loss of chemical fertilizers leads to eutrophication of water bodies, pesticides kill aquatic organisms, and livestock and poultry wastewater contains high concentrations of ammonia nitrogen. Water samplers are needed to collect water samples around farmlands for monitoring total nitrogen and total phosphorus.
Other activities: The reservoir slows down the water flow and promotes the reproduction of algae. Oil leakage from ships/vehicles hinders DO exchange. Leftover feed in aquaculture increases organic matter. Water samplers are needed to collect water samples from the corresponding areas to assess the impact.
3. The dominant causes of different water samples and their correlation with sampling
Surface water (rivers) : The main causes are domestic sewage, agricultural non-point sources and runoff. Water samplers take water samples from the river section to monitor turbidity and ammonia nitrogen, and determine whether it is black and odorous or has algal blooms.
Groundwater: The main causes are industrial leakage and landfill leachate. Deep water samples are collected using water samplers to test for mineralization and heavy metals.
Drinking water (pipeline network) : The main causes are substandard treatment and rusting of the pipeline network. Water samplers take water samples from the end of the pipeline network to monitor residual chlorine and Escherichia coli.
Industrial wastewater: The main causes are production discharge and treatment defects. Wastewater samples are collected using water samplers to test for COD, heavy metals, and pH.
Seawater: The main causes are nearshore discharge, oil leakage, and red tides. Water samplers are used to collect nearshore water samples to monitor oil content and salinity.