Ecological Technologies 47
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Ecological technologies 47 NEW APPROACH TO PREDICTING CHANGE IN AQUATIC ECOSYSTEMS WITHOUT HAVING LONG-TERM MONITORING DATA Gabyshev V.A. Institute for Biological Problems of Cryolithozone SB RAS, Yakutsk, e-mail: [email protected] This work presents an analytical approach to predicting change in the components of aquatic ecosystems. The approach makes it possible to use hydrobiological data that covers a vast geographical region without long-term monitoring data. To address the absence of long-term data we suggest using space-for-time substitution approach whereby space and time variations are equivalent. It helps to have a “time scale” from geographical latitude of sampling points. Time series received are supposed to be used for prediction models’ creation using artificial neural network method. New approach approbation was carried out upon original data on phytoplankton of 12 Eastern Siberia large rivers within 2000-2011. Three variables that had been previously found the strongest statistical re- lationship with climatic parameters were chosen as predictable indicators of phytoplankton: number of species/ number of families ratio, mean algal cells volume and total number of species in the sample. The prediction of these indicators changes was made, and the biological significance of neural network models was obtained as a result of this research. The main advantages and disadvantages of the approach were determined. Keywords: prediction approach, space-for-time substitution, artificial neural network, alternative to long-term studies, climate change, phytoplankton, Large Subarctic Rivers, Eastern Siberia, Far North According to IPCC assessment report, dur- show that the formation of the spatial structure ing the 20th century the average annual tem- of phytoplankton in the rivers of NorthEastern perature at the surface of the Earth increased Siberia occurs mainly under the influence of by 0.6 °, the ice cover duration of inland wa- climate. ters in the middle and high latitudes of the The aim of this research is to propose an northern hemisphere decreased by 2 weeks [1]. approach to predicting change in the compo- Issues of assessment and prediction of changes nents of aquatic ecosystems due to global cli- in the structure of aquatic ecosystem commu- mate change in the absence of long-term data, nities become more relevant due to global cli- exemplified by the phytoplankton of large riv- mate change. Obviously, the basis for building ers of Eastern Siberia. predictable models is the database obtained as a result of long-term monitoring observations. Materials and methods of research But due to the remoteness and inaccessibility As the material for this publication we use for researchers at the vast areas of Far North, the data on phytoplankton of 12 large rivers of there is a lack or complete absence of long- Eastern Siberia: Lena, Vilyui, Kolyma, Aldan, term data on aquatic ecosystems. In contrast Olenyok, Vitim, Indigirka, Amga, Olyokma, according to a number of researchers, trans- Anabar, Yana and Chara (Fig.1). The study formations caused by global climatic changes area lies from 106 ° 53’ to 160 ° 58’ E in the may be the most dramatic in northern regions meridional direction, and from 56 ° 13’ to 73 ° with continuous spread of permafrost [2]. East- 10’ N in latitudinal direction. 800 plankton ern Siberia is among these. algological samples were collected in 2000- We discuss the aspects of the spatial floris- 2011 from rivers both near banks and at mid- tic and coenotic structure of the largest rivers of dle course, within the surface water level (0- Eastern Siberia phytoplankton in our last pub- 0.3 m of depth), during the summer runoff low lication [3]. The materials that guide the study (June-August) at the maximum phytoplankton are an array of data on the phytoplankton of 12 vegetation period. Collection and processing large subarctic rivers, their hydrochemical, hy- of phytoplankton samples were carried out ac- drological and morphometric parameters and cording with the methods of hydrobiology [4]. climatic characteristics of the catchment areas. The analyzed data set includes 3 quantita- The information we obtained on phytoplank- tive variables: number of species/number of ton has a wide geographical scale, but was not families ratio, mean algal cells volume (μm 3) monitored, instead was selected on the rivers and total number of species in the sample. The of Eastern Siberia in different years during the data set contains only 303 observations (cases), summer runoff low. From this the most impor- which have no omissions that are inadmissible tant factors of the environment involved in the in the statistical data processing. phytoplankton of large subarctic rivers spatial The statistical analysis procedures were per- structure formation in the gamma-diversity formed in Statistica Automated Neural Networks scale were identified. The results we obtained (SANN) of Statistica 10 software package. EUROPEAN JOURNAL OF NATURAL HISTORY № 3, 2018 48 Ecological technologies Fig. 1. Map of the studied area. References: 1 – Anabar River; 2 – Olenyok River; 3 – Lena River; 4 – Yana River; 5 – Indigirka River; 6 – Kolyma River; 7 – Vilyui River; 8 – Vitim River; 9 – Chara River; 10 – Olyokma River; 11 – Amga River; 12 – Aldan River Results of research and their discussion predictable model, we suggest a space-for-time approach. The application of this method as- The results of our previous studies re- sumes that the spatial and temporal variations vealed a special regulatory role of environment are equivalent as is known [7, 8]. climatic factors in the formation of phyto- The most important environmental factors plankton spatial structure in the Eastern Sibe- in the spatial structure formation of the river ria rivers [5]. The main ones (air temperature, phytoplankton in Eastern Siberia identified Dynamic Habitat Index, duration of ice-free earlier by us are the duration of the ice-free periods on rivers) are those regional climatic period and the average annual air temperature, factors that determine the overall ecological both change equivalently according to the “ge- stress of high-latitude habitats. The complex ographical scale” (with a decrease in the lati- of climatic parameters included in the obtained tude of sampling points) and the “time scale”, statistical models indicates an important regu- this follows from IPCC specialists’ report [1]. latory function of the vegetation period dura- From the perspective of this, when imple- tion. The main results of our research indicate menting our data to build a predictable model, that the shorter the ice-free period, the lower the absent “time scale” should be replaced with the floristic proportions of plankton, the small- the “geographical latitude of sampling points “ er the mean cell volume, the smaller the total variable. To construct the model, we chose the number of species and more in the Chlorophyta artificial neural network method [9] because of and Bacillariophyta phyla, the smaller the total neural networks ability to model nonlinear de- number of species, and the larger the number pendencies [10]. of Cyanoprokaryota [6]. The key to understand The data was entered into our analysis as the “environment-phytoplankton” model in time series ranked by decreasing latitude of the studied region, which is the important dis- sampling points. We used three indicators that criminating factor that we determined, is the has the strongest statistical dependency on the geographical latitude of sampling points. We environmental parameters as the predictable show that with increasing latitude of sampling parameters of phytoplankton [6]: number of points, the basic floristic relations are reduced, species/number of families ratio, mean algal that means the proportion of monotypic taxa cells volume and total number of species in the increases. To use this data in constructing a sample. EUROPEAN JOURNAL OF NATURAL HISTORY № 3, 2018 Ecological technologies 49 Table 1 Summary of active networks (number of species/number of families ratio) Index Networks Training per- Test perfor- Validation Training Hidden acti- Output acti- name formance mance performance algorithm vation vation 1 MLP 151-8-1 0.96 0.74 0.60 BFGS 14 Logistic Identity 4 MLP 151-8-1 0.88 0.67 0.57 BFGS 9 Tanh Logistic 5 MLP 151-8-1 0.76 0.73 0.55 BFGS 5 Exponential Tanh 2 MLP 151-3-1 0.75 0.70 0.60 BFGS 6 Logistic Identity 3 MLP 151-2-1 0.54 0.72 0.61 BFGS 6 Logistic Logistic Fig. 2. Time series projection for variable “Number of species/number of families ratio”. References: 1 – Species/families ratio; 2 – [1.MLP 151-8-1]; 3 – [2.MLP 151-3-1]; 4 – [3.MLP 151-2-1]; 5 – [4.MLP 151-8-1]; 6 – [5.MLP 151-8-1] At the first stage the predictable model in- output neurons. Networks are ranked by their cluded floristic species/families ratio. To reveal performance, which is the correlation between the data internal cyclicity an analytical method the original data series and the predictable one, of Time Series spectral (Fourier) analysis was the closer this value is to 1, the better the model. used. The results showed that within the 303 In order to predict changes in the floristic observations data pool there is a periodicity, variable outside our sample set, a time-series the value of which corresponds to 151 units. projection was constructed (Fig. 2), where each Using data on the internal periodicity and ap- next value of the time series is constructed from plying the time series regression we trained the previous values of the same time series. A 50 neural network models with the condition continuous gray curve indicates the initial data of a random subsampling method. 5 more per- series, other curves illustrate the predicted se- formance networks were left in the analysis, ries for each neural network model. As we see which will predict the analyzed series of obser- in the graph of projections, most models, in- vations (table 1).