Artificial reefs as a means of hydrobiological amelioration

B.G. Aleksandrov,  Odessa Branch  Institute of Biology of the Southern Seas NAS Ukraine, 2012

The fouling community formed on hard substrates plays an important role in the process of transformation of matter and energy of aquatic ecosystems. Up to 74% of primary production and 90% of the destruction of organic matter in the coastal marine zones is produced by fouling (Alexandras 1998).

The most complete theoretical elaboration on the interrelations of the community parameters with the geometry of hard substrates was carried out on algae (Khaylov et al., 1994). Using the volume of the closest living fouling space – VCLF, it made possible prediction of the structural-functional characteristics of invertebrates according to di­mensions of recruited surface (Alexandras Yurchenko, 2000). Transitional stage for as­sessment of the ameliorative effect of fouling – determination of quantitative relations of water quality and the characteristics of the living fouling space and its biological structure including plant and animal components. However, these absolute values did not take into account their actual amount in the water. For overcoming this disadvantage and for more convenient estimations, it was proposed to assess the relations of absolute values of water quality beyond and within the limits of VCLF- These were the results of observations obtained by experts from Odessa Branch Institute of Biology of Southern Seas, National Academy of Sciences of Ukraine in 1991 – 1998 in freshwater and marine areas of the NWBS. About 1664 water samples were analyzed for 11 water quality indices and 1682 samples of phyto- and zoobenthos fouling were studied.

It has been established that an increase in the specific surface of hard substrate aids in in­creasing the total biomass of invertebrate fouling and in intensifying the self-purifying quality of the water due to respiratory functioning. The ratios received with high degree magnitude (up to 95%) allow predicting the structural-functional characteristics of the community at dif­ferent levels of saturation of the aquatic environment of the hard substrate (Table 5.1). For ex­ample, if the value of the relation of the hard substrate surface to the bottom area on which it is located (S/So) is equal to one, then it is quite possible that the fouling biomass will reach 277 g of dry ash-free matter per one cubic meter of the volume of living space. The daily intensity of self-purification due to catabolism of organic matter during respiration is 2.9 g Corg.

For vclf a decrease in content of mineral phosphorus, particulate organic matter and increase in oxygen saturation of the water has been noted. In contrast to all studied indi­ces, changes in the oxygen regime were insignificant and did not exceed 80% saturation. At the same time due to predominating functional impact of invertebrate fouling there was an increase in the total nitrogen content due to metabolic excretions in animals. The depositing of phosphates on the bed with faeces and pseudofaeces of filtering mollusks mitigates the threat of eutrophication (Alexandras 2001).

Evidence for this is the balance between nitrogen and phosphorus. Close to the foul­ing surfaces their relation was quite stable in spite of the 10 fold variations in absolute values. The high range in variability of environmental indices – up to a magnitude of 3 for which equations were established allowed considering the relation of the rate of trans­formation of fouling and the pollutant concentration (Table 5.2).

Table 5.1. Parameters of relations of the species IgY = Ig a + b Ig X between the characteristics of structural-functional organization of the fouling community, its living space and ameliorative impact on aquatic environment (Aleksandrov, 2008)

 

Relations

n

r Ig a b
DWz = f (CS)

43

    0,64*

-0,104 ± 0,477

0,846 ± 0,157

R = f (CS)

42

    0,55*

-0,563 ± 0,563

0,830 ± 0,201

Ptot = f (VCLF)

46

    0,34*

-0,459 ± 0,124

0,040 ± 0,016

DWZ = f (S/S0)

43

    0,89*

-0,557 ± 0,288

1,112 ± 0,091

R = f (S/S0)

42

    0,91*

-0,883 ± 0,275

1,223 ± 0,087

VCLF/Vf = f (S/S0)

42

   -0,76*

-1,342 ± 0,463

   -1,087 ± 0,146

S/Vf = f (S/S0)

42

   -0,35*

-1,940 ± 0,469

   -0,328 ± 0,148

Sph/Vf = f (S/S0)

42

   -0,17

-0,553 ± 0,433

   -0,153 ± 0,137

Nmin = f (S/S0)

46

   -0,30*

-0,166 ± 0,159

   -0,091 ± 0,043

Ntot = f (S/S0)

42

   -0,44*

-0,258 ± 0,163

   -0,158 ± 0,051

Ptot = f (S/S0)

42

    0,27

  0,022 ± 0,127

0,065 ± 0,035

O% = f (S/S0)

42

   -0,35*

-0,039 ± 0,053

   -0,040 ± 0,017

POM = f (S/S0)

41

    0,31

0,313 ± 0,281

0,186 ± 0,090

Pph = f (S/S0)

46

   -0,18

-0,003 ± 0,569

   -0,187 ± 0,156

Nmin = f (DWZ)

42

   -0,50*

-0,322 ± 0,147

   -0,139 ± 0,038

Ntot = f (DWZ)

42

   -0,53*

-0,369 ± 0,153

   -0,158 ± 0,039

O% = f (DWZ)

42

   -0,36*

-0,056 ± 0,053

   -0,033 ± 0,014

POM = f (DWZ)

41

    0,35*

 0,407 ± 0,278

0,166 ± 0,072

Nbac = f (DWZ)

41

  – 0,11

-0,115 ± 0,238

   -0,044 ± 0,063

BOD5 = f (Sph/Vf)

42

   -0,11

-0,088 ± 0,208

   -0,052 ± 0,075

Note: * – critical value for r for 5 % significance level (significant for 95% confidence). Indices; 1) living space of fouling: VCLF – volume of closest living space, cm2; Cs – specific surface of hard substrate (concentration of fouling surface in volume of living space), S/VCLF x nrr1, S/So – coefficient of packing of hard substrate (total area of hard substrate to area of bottom on which it is based); 2) structural-functional organization of foul­ing: DWZ -total biomass of dry free ash matter of invertebrate fouling according to VCLF, mg x cm3, R – respiration intensity, Jxcnrr3 x dienrr1, Vf — daily intensity of water filtration by fouling according to vclf / s and Sph – photosynthetic surface of algae and macro-phytes; 3) ameliorative effect: Nmin – mineral nitrogen content, Ntot – total nitrogen, Ptot – total phosphorus, O % - saturation of water with oxygen, POM – particular organic matter, PPh – phytoplankton production, Nbac – total microbe number, BOD5 – biochem­ical oxygen demand (ameliorative effect is evaluated according to the relation of the absolute values of water quality beyond and within the limits of CLF).

When forecasting the ameliorative fouling effect the features of the biological structure should be taken into consideration. The presence of animal filtrators is char­acteristic to climax communities, which leads to a large increase in VCLF defined as “the geometric water volume within the limits of the fouling contour” (Khaylov et al., 1994).

When comparing literature data with estimations of the ameliorative effect calculat­ed according to the formula POM = 2.553-DW0166, (see Table 5.1) the prognostic capac­ity of phyto- and bacterioplankton was evident. The difference between prognostic and a definite value of self-purifying capacity of an artificial reef by heterotrophic bacteria reached 12% for mussel fouling at a depth of 5 m and 38% at a depth of 10 m (Govorin et al., 1994).

The values received (see Table 5.1) can be used for determining the optimal parame­ters of artificial substrates with ameliorative effect when creating hydrotechnical structures of different designation (Alexandrov, 2001)

Table 5.2. Range of indices of studied characteristics

 

      Range of values
  Characteristics*    Dimension min max       max/min

Living space

VCLF

cm3

7,42 . IO9

1,38 . IO12

186

S

cm2

8,32 . IO6

2,11 . IO9

254

S0

cm2

5,12 . IO7

1,79 . IO10

350

Fouling community (values of characteristics reduce to square meter of hard substrate)

DWph

г

1,6             169,9

106

DWZ

г

107,8           1282,3

12

R

kJ . day-1

40,0            769,0

19

            Sph

m2

          1,9              45,1

24

Water quality

Nmin

μg . I-1

50,000

1952,000

39

Ntot

μg . I-1

397,000

8323,000

21

Ptot

μg . I-1

19,000

300,000

16

O %

%

82,000

182,000

2

POM

g С . m-3

0,280

  7,350

26

Pph

g С .m-3 . day-1

0,001

  2,199

        2199

Nbac

mln. cell. ml-1

0,900         506,600          563

BOD5

mg О . I-1

0,110

  3,940

36

Note: * – definitions in previous table, DWph – biomass of dry ash free matter of macrophytobenthos