NUTRIENT STATUS AND PLANKTON OF NEARSHORE WATER AREA OF KRONOTSKY GULF IN AUGUST 2015

Received: 15.08.2016 Firstly we carried out a hydrological and hydrobiological study of the nearshore area, at a depth up to 15 m of Kronotsky Gulf (Kronotsky Reserve, Kamchatka). We have shown that the washout from rivers influences significantly the hydrochemical status of nearshore areas. This parameter determines the level of organic and mineral forms in the compound of phosphorus and nitrogen pools and the content of iron in sea water. The hydrochemical status (particularly – the content of organic compounds) influences the structure of phytoplankton. Diatoms dominate in the locations with relatively high concentrations of mineral forms of phosphorus and nitrogen. In locations with an increased level of these elements in the contents of organic compounds, heterotrophic dinophytes and rotifers dominate. Lists of species of phytoand zooplankton and their quantitative assessment are presented.

The Kronotsky State Biospheric Reserve includes the 4.8 km long nearshore area of Kronotsky gulf with a depth up to 100 m.During expeditions of the Institute for Oceanology AS USSR in spring 1951-1955, a complex study of Kronotsky gulf was carried out to evaluate its commercial fishing importance.During these expeditions, a bathymetrical map of the gulf was compiled, the bottom configuration (Kanaev, 1959) and bottom sediments (Petelin, 1959) were described, a hydrological characteristic was provided (Gamutilov, 1959).Also, a specific composition of phyto-, zoo-and ichthyoplankton and zoobenthos in the gulf was found in general.Their quantitative assessment and spatial distribution were studied (Semina, 1956(Semina, , 1959;;Lubni-Gertsik, 1959;Ponomareva, 1959;Kuznetsov, 1959;Khrapkova, 1959;Polutov & Vasiljev, 1959).However, data of those important investigations were obtained more than 60 years ago and -only for a spring season (April -May) and bordered by >30 m isobaths, excluding the littoral zone.
Therefore, in 2015 a hydrological and hydrobiological monitoring of the nearshore area of Kronotsky gulf started, carrying out a long-term monitoring of its ecological conditions and revealing natural and anthropogenic factors which influence the biota of coastal shallow water.
Subsequently, on 15-16 August 2015 series of hydrochemical and hydrobiological samples were collected.To determine the nutrient status water samples were collected from the water surface.Then they were fixed with chloroform and were kept at a dark and cool place in order to conduct the posterior laboratory analysis.Phosphate phosphorus (PO 4 ), total phosphorus (TP) and nitrogen (TN), mineral forms of nitrogen (ammonium -NH 4 , nitrites -NO 2 , nitrates -NO 3 ), total iron and dissolved silicon were detected in the water samples, using standard methods (Handbook, 2003).Organic forms of nitrogen (ON) and phosphorus (OP) were calculated by subtraction of mineral components from the total concentration of the proper element.Samples of plankton were collected with an Apshtaine net (D = 18 cm, nylon stocking with cell size 76 μm) in the nearshore zone (depth < 20 m), in the bottomsurface layer.A description of the samples is presented in Table 1, the location of stations in Fig. 1.
NUTRIENT STATUS.A graphic interpretation of data on nutrients in the surface layer of the nearshore area of Kronotsky gulf is presented in Fig. 2. In miniprofiles of estuaries of the rivers Olga and Kronotskaya, we found that a reduction of the washout influence and a decrease of the concentration of nutrients (including Fe) take place in relation to the distance from the river estuary.At these locations 50% of TP was presented by the organic phosphorus component.Similar results were found for a phosphorus pool at the Kozlova point.On the contrary, 70-80% of phosphorus was mineral in the rivers Stolbovaya and Tjushevka, and in the outlet to the sea station at the river Olga (Fig. 2A).nitrogen were estimated at 40% and 30% respectively (Fig. 2B).From 70% to 90% of mineral forms of nitrogen accounted for the reduced ammonium form (Fig. 2C).This is no surprise taking into account the structure of the nitrogen pool with dominating organic compounds.

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About 10% of the nitrogen pool is a sum of mineral forms; the other 90% is nitrogen as a part of organic compounds.The exceptions are the station in the estuary of the river Stolbovaya and the station at the outlet to the sea in the river Kronotskaya: the concentrations of mineral and organic The highest outlet of total iron was found in the river Tjushevka.Perhaps, this is associated with discharging of Tjushevskiye's hot springs to the river.Concentrations of this element were three times less in the rivers Stolbovaya and Olga.The concentration of iron in the zone under influence of the river Kronotskaya and the Kozlova rock was equal to analytic zero (0.02 mg Fe/l) or little more.Most of the silicon is washed out by the river Kronotskaya (Fig. 2D).
PHYTOPLANKTON.We have registered 62 taxa of microalgae.Diatomic microalgae (Bacillariophyceae) dominate in the species composition (46 species; 74% of the total number of species).Amongst them, typical marine algae are: Numerically (30,000-100,000 cells/m 3 ) diatoms also dominated in plankton.These algae were the most abundant in the river Tjushevka estuary where the highest Fe concentration was registered in the water.
The number of dinophytes was two times less.Their highest concentrations were registered in the estuaries of the rivers Olga and Kronotskaya (Fig. 3), at stations in the close vicinity of estuaries, at the locations with the highest content of nitrogen and phosphorus in organic compounds.
At stations with abundant dinophytes (estuaries of the rivers Kronotskaya and Olga), a dominating complex was formed mainly by species of the genera Ceratium F. Schrank (400-3,600 cells/m 3 , and 1,300 cells/m 3 in average) and Gymnodinium (700-4,800 cells/m 3 , and 4,100 cells/m 3 in average).In the waters with a low number of dinophytes, representatives of the heterotrophyс genus Protoperidinium R.S. Bergh were the most numerous.
The contents of nitrogen in the organic matter was the highest in the river Olga outlet.Zooplankton was highly represented in waters at this location.Rotifers dominate there, and copepods are subdominant.Zooplankton was formed by copepods and larvae of sea-urchins in equal shares.Its quantity was three times lower in the river Stolbovaya estuary (Table 2, Fig. 4).Factual material represented above does not allow making unambiguous conclusions on stable patterns of biogenic background, specific composition and plankton diversity, and productivity of separate water areas at the nearshore of Kronotsky gulf.Further investigations within the frameworks of long-term monitoring (successions, regularity, continuity) using standard methods are needed for that.

Fig. 1 .
Fig. 1.Schematic map of sampling area in the nearshore area of Kronotsky gulf in August 2015.

Table 1 .
Description of hydrological and hydrobiologycal samples from Kronotsky gulf on 15-16 August 2015 №Longitude Latitude Depth (in m) Comments 1 160.7323254.518526The Kronotskaya river mouth, 300 m from the shore, just past the eagre (external edge of cone delta)