**3.3 Biological indices**

There are many biological indices for water quality assessment, which may depend either on many parameters or on a particular one. The algal periphyton system, in terms of similarity, diversity, evenness, structure, and dominance, has been employed in the construction of a variety of biological indices of both kinds [154–156]. There has been criticism regarding the processes, which reduces the indices to a single quantitative or qualitative result regarding its representational effect [157] due to seasonal variability [158–161] or regionality [162, 163]. Despite the objections, this type of indices has been employed in many countries including the U.K., the U.S.A, Spain, and Canada. Most countries have passed legislation according to which government entities controlling rivers and water bodies in general are obliged to use biological indices, for example, Italy [164], in order to assess stream condition in terms of water quality and water abstraction impact [7]. The European Water Framework Directive [165] included biological monitoring as a stream health assessment tool, and in the U.S.A., macroinvertebrate community assessment is used under the Clean Water Act [166].

Biological indices are used by conjunctive employment with multivariate statistical analysis, which leads to a good understanding of aquatic biota-sensitivity and to the determination of the driver-response relationship [7, 91, 167–169]. Biological indices resulting from multivariate analysis techniques are as follows:

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


Multi-metric techniques (biotic integrity indices) [182] are employed as an approach where an integrated balance is maintained in adaptive biological systems between elements and processes such as species, genus, assemblage and biotic interaction, nutrient and energy dynamic, meta-population process respectively in natural habitats [183, 184]. The initial concept of biotic integrity, the Index of Biotic Integrity (IBI) has been developed for fish in shallow rivers [185] in the USA measuring trophic composition, species composition, and abundance and health of fish [183, 186], and Karr's work is reevaluated in Capmourteres et al. [187]. According to Gordon et al. [7], in the case of the biotic integrity index small disturbance to the system has negligible effect on the biological integrity of the system, which was one of the presuppositions of its design [185]. However, a unified conclusion regarding the regularity of different group-based IBI evaluation results has not been reached [188–190] as seen in Huang et al. [191]. Various biotic integrity-based biotic indices besides IBI exist:


(precision, range, responsiveness to disturbance, relationship to catchment area, and redundancy with respect to other metrics), while a continuous scale is employed for scoring [203].

### **3.4 Riverine ecological assessment: The role of algae**

Algae are in general one of the primary producers in aquatic ecosystems [204, 205] taking into consideration that Water N:P molar ratios could result in being restrictive for river algal communities' population dynamics and species coexistence [206].

Algae react to riverine ecosystem disturbances and show sensitivity to changes in environmental conditions [29, 126, 150, 207–214]. However, riverine algae are not as sensitive to changes in environmental conditions as periphytic algae, which grow by substrate attachment, and in case of negative environmental changes move away [215].

In effect, they have the characteristics necessary to become prime environmental conditions monitors in aquatic ecosystems at a global applicative level [28, 29, 90, 108, 126, 216–221]. In particular, their properties [120, 220, 222, 223] are seen below:


Community structure, biomass standing crop, and species composition have been employed in the assessment of riverine ecological condition both directly and indirectly [224–227]. Riverine biofilm structure [125, 207, 228–232] and ecosystem processes [151] have been shown to be affected by flow variation. Within the biofilm, diatom algal assemblages within the biofilm are highly responsive to water chemistry variations [152], and consequently, their composition can give away any ecological responses to flow-driven changes occurring in stream water quality. Using algae as an ecological state assessment tool leads to the detection of harmful riverine ecosystem human activity [126, 233, 234], providing thus the evidence necessary for carrying out water resource managerial decisions.

Flow current exerts influence over algal immigration [235], reproduction by varying nutrient supply rates [236], and community physiognomy by decreasing attachment strength [237].

High stream discharge velocities may affect benthic algae in different ways, which depend on both frequency and intensity [238, 239] and change both physiological and structural properties of the community [240, 241].

In lotic and lentic freshwater ecosystems, algae are the main primary producers as, for example, trophic status *via* the trophic state index (TSI) is determined by algal levels [242], seen in Round [243], Stevenson et al. [244], and Allan and Castillo [245] and being the main source of energy for first-order consumers such as small herbivores places them in an important role in the food web. Algae growth is dependent on riverine nutrient concentration, mainly on phosphorus and nitrogen, and also on benthosconcentrated ones [244, 246], while other factors, such as predation and hydrology, have a significant contribution [141, 244, 247–250].

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

As seen in Steinman [251], there are various forms of benthic algae assembly, for example, stalked (colonial) aggregates, unicellular states [252], and filamentous [253]. Benthic algal biomass constitutes an excellent water quality indicator [254–257] and, through that, of river condition and therefore health [258]. Algal biomass analyses are often used for river health evaluation [259] as well as of riverine ecosystems anthropogenic modifications analysis, for example, of dry mass [260], of chlorophyll-*a* concentration [261–263], bio-volume and peak biomass [244, 260, 264], and ash-free dry mass.

The flow regime, stream velocity in effect, is in negative correlation negatively with chlorophyll-*a* concentration [228, 265, 266]. While chlorophyll-*a* concentration tends to increase downstream in a state of constant flow, there are also upstreamcaused downstream effects [267]. The flow-related disturbance effect on biomass is also [228, 265, 266, 268–270] as well as in rainforest streams [271] and in the creation of gradient of metacommunity types within stream networks [272]. Algal biomass is seen to decrease due to suspended solids and grazers, that is, fish and invertebrates, substratum instability, flow disturbance, that is, velocity where stream algal biomass responds to nutrient enrichment depending on the velocity [273]. Conversely, light, temperature, and nutrients are seen to be the main promoting resources of algal biomass [141, 274].

Νutrients as well as grazing pressure and light influence algal growth and community structure [275, 276]. In terms of algal biomass control, the main top-down controllers are nutrients and light are top-down and grazers, mainly fish and snails, are the main bottom-up [207, 251, 277], while under certain conditions there is feedback between the two processes [278]. A controller of algal community structure is lotic system flow disturbance [245, 279–281].

Shifts in water quality and flow variation affect algal colonization and structure [125, 228, 245, 282–285]. Flow regime impacts on both water quality, that is, temperature, suspended solids, oxygen level, organic matters, and other nutrients in general, and the metabolism of rivers or streams and biotic structure and function [7, 149, 286, 287]. Climate change impacts water quality [288], and as seen in Baron et al. [289], environmental factors impact the structure and function of aquatic ecosystems and flow regimes, sediment and organic materials, water quality, nutrients and other chemicals elements, light, temperature, for example, "brownification" where, as seen in De Wit et al. [290], a 10% increase in precipitation will result in increasing by 30% the soil transfer of OC to freshwaters.

The list of environmental factors affecting the structure and function of benthic algae in riverine ecosystems was compiled and analyzed, in particular grazers, temperature, pH, light, hydraulics, and nutrients (N, P, Si). While, under fast flow and low nutrients algal community structure, species composition, biomass, and standing crop decrease slow flow and a high concentration of nutrients increase algal biomass and community structure.

Climate variability/change is seen to affect algae directly [291–294]. As seen in Sinha and Michalak [295], precipitation, which is climate induced, is a preeminent factor in the variability of riverine nitrogen. Moreover, precipitation plays a role in algae affecting stream flow velocity [296, 297] as seen in the Heavy Precipitation Index [298], which is a part of the Streamflow Indicator as defined in [299]. This makes the climate/precipitation mechanisms in [300–303], and flood events [304] lead to effects, which influence algae in an important and multifaceted way.
