**5. Physico-chemical characteristics of lotic ecosystems**

### **5.1 Currents and stream pattern**

Running waters' gradient and substrates have an impact on the current's speed. Wind has little effect on currents in running waterways, in contrast to lentic waters. The properties of the drainage basin are what determine how water, dissolved chemicals, and suspended particles travel continuously downstream. According to this gradient, there are numerous stream patterns, including dendritic, rectangular, radial, trellised, parallel, annular, deranged, and pinnate. The risks of soil erosion are determined by the stream pattern.

## **5.2 Light**

Light is important to lotic systems, because it provides the energy necessary to drive primary production via photosynthesis, and can also provide refuge for prey species in shadows it casts. The amount of light that a system receives can be related to a combination of internal and external stream variables [23]. The presence of turbidity has a significant impact on how well light penetrates moving waters. There is a loss due to water absorption in addition to scattering by particles. A sufficient amount of light can reach the substrate and enable photosynthesis if the water is transparent or hollow. The availability of light may also be affected by seasonal and nocturnal circumstances because the angle of incidence—or the angle at which light strikes water—can cause light to be reflected back into space [24].

### **5.3 Temperature**

Temperature is a crucial abiotic component for most lotic species since they are poikilotherms, whose internal temperature fluctuates with their surroundings. Water can be heated or cooled through surface radiation, conduction to or from the air, and other nearby substrates [24]. The absence of temperature-related stratification means that a stream's temperature follows that of the surrounding air because of increased interaction with it. Numerous variables, including as the source, depth, substrate, tributaries, exposure, and time of day, affect the temperature of lotic water. The contribution of surface and ground waters to stream flow varies depending on a number of variables, including the geology and temperature of the area. Running water fuelled mostly by surface runoff has variable flow and may spate after each significant downpour, whereas running water fed primarily by ground water often has regular flow.

### **5.4 Dissolved gases**

The most prevalent and significant dissolved gas in flowing water is oxygen. Due to turbulence and mixing, there is a high concentration of oxygen. Organic

contamination is typically indicated by low concentration. However, the oxygen concentration in the diurnal basis varies. Current, water temperature, and the presence of breathing plants and animals all affect how much oxygen is present. The carbon-di-oxide concentration of the moving waters tend to be sparse due to constant turbulence of water and its frequent interaction with air [3].

### **6. Distribution of planktonic forms in lentic and lotic systems**

Plankton distribution patterns and environmental conditions are closely connected. Climate, water, temperature, light intensity, nutrient concentration, river shape, discharge, water residence time, precipitation, and biotic variables are examples of potential physical, chemical, and hydrological elements [25]. All the creatures suspended in unrestricted water are referred to as plankton. Aquatic organisms that drift passively and have limited ability to move in opposition to the movement of the water mass make up the plankton. Compared to benthic or nektonic species, planktonic organisms have a short life cycle and high metabolic activity, which allows them to respond to any pollution challenge quickly and dramatically [26]. Hence, study of planktonic community is of crucial importance in understanding pelagic productivity and pollution impacts [2].

Phytoplankton and zooplankton are two types of plankton. All suspended microalgae in a body of water that belong to all taxonomic algal groups are referred to be phytoplankton [27]. The primary producers in aquatic habitats and the foundation of the food chain are phytoplankton and other aquatic plant life [28]. Zooplankton, the animal element of the plankton, is a vital component of a freshwater ecosystem's food chain since it occupy a central position between of autotrophs and other heterotrophs. All varieties of aquatic bodies exhibit zooplankton abundance due to energy transfer occurring at various trophic levels [9].

Pelagic creatures known as zooplankton are those that are unable to hold their location by swimming against the physical movement of water [29]. They were found in practically all water bodies, including rivers, streams, lakes, reservoirs, ponds, irrigation canals, rice fields, and temporary water bodies. They lived in both freshwater and saltwater. By regulating phytoplankton production and modifying the pelagic ecology, zooplankton play a crucial role in the pelagic food web. They are heterotrophic animals unable to produce organic materials on their own [30].

Water currents transport zooplankton from lentic to lotic systems, and the energy in their tissues can change resource availability downstream, changing ecosystem functioning and the community structure of lotic consumers [31]. As essential biotic components of the food webs in any body of water, zooplankton diversity and abundance play a crucial role in the establishment of water quality and trophic levels as well as serving as the subject of bioindication and environmental condition monitoring [32]. The zooplankton community is quite susceptible to changes in the environment. Therefore, they are of ecological relevance because changes in their abundance, species diversity, or community composition can give key signs of environmental change or disturbance [10].

#### **7. Primary productivity of lentic and lotic ecosystem**

Any aquatic ecosystem's main production is based on the diversity of planktonic organisms. A water body's primary productivity estimate can be used to determine

#### *Zooplankton Productivity Evaluation of Lentic and Lotic Ecosystem DOI: http://dx.doi.org/10.5772/intechopen.107020*

how much biological population it can support through respiration. It is the most significant biological phenomenon, on which all forms of life are directly or indirectly dependent [11]. The amount of primary production must be determined in order to gauge a reservoir's bioactivity. Production is the measure of how much solar energy is captured by autotrophic organisms. Productivity is the solar energy captured by autotrophic organisms per unit of time [33]. The rate at which radiant energy is stored by a producer's photosynthetic and chemosynthetic processes is referred to as primary productivity [34]. The most significant biological phenomenon in nature is primary productivity, which is directly or indirectly dependent on the entire biodiversity. Through the process of photosynthesis, primary producers generate organic matter from inorganic nutrients. Primary producers need essential nutrients to live and grow such as nitrogen, phosphorus, magnesium, calcium, iron, zinc, etc. in sufficient amount. Phytoplankton, Macrophytes, and Periphyton are the main producer in lake and reservoir [35].

Primary producers require appropriate amounts of key nutrients including nitrogen, phosphorus, magnesium, calcium, iron, and zinc to survive and flourish. The primary producers in lakes and reservoirs include phytoplankton, macrophytes, and periphyton [36]. The balance between gross photosynthesis, respiration, and other plant losses, such as death, is referred to as net primary productivity. There are several characteristics of primary production in aquatic ecosystems that are different from those in terrestrial systems. Contrary to nutrients, which may go through multiple cycles, the movement of energy through an ecosystem is a one-way process. The primary productivity is the foundation of all food chains and food webs in each ecosystem, and it also produces 70% of the world's atmospheric oxygen. Note that the efficiency with which energy is converted by organisms into other forms (chemical energy) and the quality of incident solar energy per unit area of the ecosystem are the two main concerns of ecologists interested in ecoenergetics and the study of productivity, which is currently receiving much attention in ecology [37].

The productivity of a water body is determined by the quantity of plankton present within. When compared to lotic water, lentic water has the highest primary productivity. This suggests that lentic water has more planktonic activity. The "light and dark bottle method" was used to determine the primary organic output of the river water. The method of measuring the production and consumption of oxygen using light and dark bottles and Winkler's titration was initially put forth by Gaarder and Gran in 1927 [38]. It is the most typical technique for assessing output and productivity in the aquatic environment. The amount of dissolved (or free) oxygen in water or wastewater is measured. The amount of dissolved gas (oxygen) per litre of water is known as the dissolved oxygen concentration. In this method, productivity is calculated by evaluating the dissolved oxygen content (**Figure 4**).

#### **8. Water productivity calculation**

The following formulas were used to compute Gross Primary Productivity (GPP), Net Primary Productivity (NPP), and Respiration:

$$\text{Gross Premary Productity} = \frac{LB - DB}{\text{T}} \text{X} \frac{0.375}{PQ} \text{X } 10000 \text{mg / L / h}$$

**Figure 4.** *Schematic representation of productivity of aquatic system.*

$$\text{NetPrimary Productity} = \frac{LB - IB}{\text{T}} \text{X} \frac{0.375}{PQ} \text{X 1000} \text{mg/L / h}$$

$$Respiration = \frac{IB - DB}{\text{T}} \text{X} \frac{0.375}{PQ} \text{X } 1000 \text{mg/L / h}$$

Where:

LB = Light bottle, DB = Dark bottle, IB = Initial bottle, T = Time of incubation, PQ = Photosynthesis Quotient = 1.25, RQ = Respiratory Quotient =1 and. The value 0.375 represents a constant to convert Oxygen value to Carbon Value.
