**3.2 Biological monitoring systems**

Biological monitoring systems are usually based on fish, benthic macro-invertebrates as well as macrophytes, riparian vegetation, and algae [7, 77–91].

In determining water quality from the assessment of river ecosystem health, macro-invertebrates are considered to be both important, as they are a critical part of the aquatic food framework [92] and preferable to other targets for the following reasons [93]:


*Monitoring of Rivers and Streams Conditions Using Biological Indices with Emphasis on Algae… DOI: http://dx.doi.org/10.5772/intechopen.105749*

Generally, in-stream biomonitoring can be employed using some or all of the aforesaid macro- and micro-organisms as biological indicators/indices. However, from the point of view of spatial and temporal invariance this leads to problems.

Benthic macro-invertebrates are used by a large number of scientists because they are sensitive to water degradation and river health and depend on sediment quality [103]. A major issue is eutrophication, "*excessive plant and algal growth due to the increased availability of one or more limiting growth factors needed for photosynthesis*" [104], which usually occurs in rivers that are passing through urbanized/agricultural areas [105] and seems to depend strongly on the local stream and its surroundings characteristics [106] in case of which both reaction and response become limited [107, 108]. Another issue is that in order to assess human-influenced events separately from the naturally caused ones, that is, natural seasonal or successional variation [109], a stressor-specific multimetric approach is needed [110].

In a 2008 statistical analysis [111], the findings were as below:


In rivers where macrophytes are not abundant, bottom-lying biofilm is the main agent of nutrient uptake, a stratum that consists [112] of algae, bacteria, and fungi ensconced in a polysaccharide matrix. In the case of nutrient change, algae react directly but invertebrates generally respond indirectly depending on the water quality intensity of influence on the habitat. The mechanism explaining this [113, 114] is that an initial subsidy effect consisting of increasing nutrients leads to the direct stimulation of algal productivity and this, in the role of a mediator, causes, through increased trophic resources, the macroinvertebrate's response stimulation. For this reason, some approaches to understanding river conditions have been based on As algal biofilm/ diatom communities are sensitive and responsive to river physical, chemical, and biological changes [24, 29, 115–118] and there are a lot of approaches for river condition assessment based on them.

Biofilms are a major element of river food webs [119] and important for stream biogeochemical and nutrient processes [120–126]. Microalgae are the main food source for fauna in freshwater ecosystems. Algae-based processes lead to the production and synthesis of organic matter (carbon) and allow its entry into the food web *via* which is available to higher trophic consumers such as fish and waterbirds [127–129], and consequently, algae, in terms of freshwater ecosystems [126], are considered to be the most essential part of food webs and biogeochemical cycling, for example, carbon

cycling [130]. Epiphytic algae are one of the appropriate food sources for stream invertebrates in an interactive way [131] since freshwater algae carry high concentrations of polyunsaturated fatty acids and in stream food webs, high-quality algae enhances the food value of low-quality riparian leaf litter [129, 132, 133]. In terms of algal groups, diatoms and cryptophytes supply aquatic invertebrate food of higher quality due to long-chain omega-3 polyunsaturated fatty acids [132, 134–136], while omega-3 (n-3) long-chain essential fatty acids (EFA) are higher in running water than brackish [136] and are projected to decrease as world temperature rises [137]. As these species are the important indicators of river health, their primary production is equally important and may be decreased by turbidity and shading, due to light blocking [138, 139], while shear stress and low nutrients are important inhibitors particularly for algal primary production along with temperature and grazing [140].

Primary producer community structure (PPCS) in rivers and streams is influenced by the general state of hydrodynamics [141, 142] as flow velocity increase is correlated positively with increased nutrient delivery by increasing PPCS productivity through thinning the diffusive boundary layer up to a point where it becomes negatively correlated due to dislodgement [143–145]. As seen in Gurnell [146], PPCS influences ecosystem structure *via* their hydrodynamics and morphology by flow-vegetationsediment feedbacks.

Algae, having increased sensitivity, often signal changes in environmental conditions by responding well before effects on higher organisms manifest themselves [29, 78]. The reduction of river flow affects biofilm structure [125], for example, in terms of causing increased algae bloom [147], which prevents sunlight from penetrating the water surface [148] as well as ecosystem processes in general [149–151]. In the biofilm structure, diatom assemblages are shown to be highly responsive to water quality variation [152] since their assemblages are used to measure water quality [153].
