EPIPHYTIC AND SEDIMENTARY IN RELATION TO PHOSPHORUS, NITROGEN AND IN NON-ACID LAKES AND PONDS (FLANDERS, BELGIUM) Luc Denys

Institute of Nature Conservation Kliniekstraat 25, B-1070 Brussel [email protected]

Very different ‘communities’ can be targetted in lake-phytobenthos Data are from 141 water bodies. Most are small (0.02-74 ha) and unstratified (Zmax. 0.5-18 m). Alkalinity monitoring (Table 1). This inevitably affects the perception of ecological ranges from 0.1 to 5.2 meq l-1, pH from 6.5 to 9.3, EC from 190 to 3520 µS cm-1, chl a from < 3 to 310 µg l-1 -1 status. Here, the response of diatoms in superficial littoral surface sediment and TP from < 70 to 2.890 µg l . Unless otherwise indicated, values for water-column variables are medians of 3-6 measurements (May-November). counts of 500 valves; 0.02 % attributed to additional taxa. and in the epiphyton to some eutrophication-related water column variables is examined, focussing on non-acid standing fresh waters in lower Belgium. 1.0 a. sediment Table 1. Some of the more prominent differences between diatom assemblages on hard substrates 1.5 b. epiphyton and in recently deposited soft sediments. epilithon and epiphyton surface sediment assemblages eigenvalue0.107= sodium surface pGOP sodium ● species richness, diversity lower higher DIC TON ● temporal integration ≤ months; lower proportion of dead cells ≤ years; larger proportion of dead cells magnesium eigenvalue0.109 = ● spatial integration mainly from in situ growth in situ growth and recruitment from TPmax. surrounding ‘mesohabitats’ calcium DIC slope ● major physical disturbances intense grazing or water movement increased sediment mobility or deposition surface COD pGOP ● substrate interactions with hard substrate or macrophyte with sediment particles and interstial water oxygen saturation ● oxygen and light regime more aerobic and euphotic environment adaptations to anaerobic and low-light conditions silica silica sand TIN ● spatial heterogeneity, patchiness higher? lower?

● phytoplankton contribution usually small can be substantial loam ● abundance of ‘opportunistic’ taxa mostly low to moderate frequently high trees & shrubs eigenvalue = 0.167 Table 2. Results of CCAs constrained to eutrophication-related variables -1.0 (transformed; with single variables, significance is for the constrained axis only). -1.5 2.0 Figure 1. CCA biplots of a. sediment assemblages and b. sediment assemblages epiphytic assemblages epiphyton with forward-selected variables (p ≤ 0.05, Bonferroni- eigenvalue = 0.142 % species data F p % species data F p -1.0 corrected). Eutrophication-related variables are in red. explained explained -1.0 1.0 TP 2.9 3.6 0.002 3.0 4.2 0.001 Trophic variables: which ones and how important are they? TPmax. 2.6 3.7 0.002 3.3 4.6 0.001 Potential gross oxygen production (pGOP), a measure for phytoplankton productivity, and chemical oxygen TON 2.9 4.2 0.001 3.1 4.3 0.001 demand (COD) are the variables associated with trophic status showing the strongest links to sediment TIN 0.9 1.3 0.054 1.2 1.6 0.005 assemblage composition (Figure 1a). Epiphytic diatoms can be related to maximum total phosphorus TN 2.1 2.9 0.001 1.9 2.6 0.001 (TPmax.), total organic nitrogen (TON), pGOP and total inorganic nitrogen (TIN) (Figure 1b). The marginal pGOP 2.9 4.2 0.001 2.1 3.0 0.001 effects of TP (either as median or maximum values), TON (substituting COD for sediment assemblages; r = chl a 2.6 3.6 0.002 1.9 2.7 0.001 0.83) and pGOP are comparable, although quite small (Table 2). TON explains more variation than total TP+TON+pGOP 7.2 3.5 0.001 7.2 3.5 0.001 nitrogen (TN) or chl a. The combined effect of TP, pGOP and TON is the same for both assemblage types, but together these variables still account for only c. 1/14th of the variation in species composition. 70 r = 0.7922, p = 00.0000 r = 0.6713, p = 0.0000 r = 0.7530, p = 00.0000 60 no relation 18 24 50 famelica sediment epiphytes Cyclotella atomus 1600 Fragilaria famelica 40 16 22 30 1400 14 Cyclotella meneghiniana 20 Achnanthidium saprophilum % of taxa 20 Nitzschia pumila Nitzschia palea Staurosira construens 1200 10 12 Gomphonema parvulum 18 f. saprophilum Nitzschia pumila Amphora veneta Planothidium engelbrechtii 0 Gomphonema utae 1000 10 16 chl a pGOP TP TPmax. TON TIN Achnanthidium saprophilum Achnanthidium exiguum 800 8 antonii Planothidium engelbrechtii 14 70 N. rhynchocephala Nitzschia dissipata Nitzschia acicularis Nitzschia filiformis Craticula buderi 600 var. media 60 increase or decrease 6 12 Nitzschia acicularis Staurosira elliptica 50 sediment epiphytes 4 400 10 40 Ulnaria ulna var. angustissima

optimum pGOP epiphyton (mg/L) 2 200 8

30 optimum TPmax epiphyton (µg /L) optimum TON in epiphyton (mg/L)

% of taxa Asterionella formosa 20 0 0 6 10 0 2 4 6 8 10 12 14 16 18 0 200 400 600 800 1000 1200 1400 1600 6 8 10 12 14 16 18 20 22 24 0 optimum pGOP sediment (mg/L) optimum TPmax sediment (µg/L) optimum TON in sediment (mg/L) chl a pGOP TP TPmax. TON TIN Figure 3. WA-optima of taxa in sediment assemblages and in the epiphyton for selected impact variables. Loess smooths in red. Wilcoxon matched pairs test: pGOP p < 0.001, 70 TPmax. p = 0.006, TON p = 0.014. 60 increase or decrease with plateau Responses at the species level 50 sediment epiphytes A larger proportion of taxa shows no clear response to eutrophication-related variables in sediment assemblages than in the epiphyton 40 30 (Figure 2). In the sediment, more taxa increase or decrease gradually along the trophic gradient, whereas epiphytes rather tend to have % of taxa 20 unimodal distribution patterns. A taxon’s apparent optimum (as its abundance-weighted average) for a specific variable may differ 10 0 considerably between both assemblage types (Figure 3); there is a tendency towards lower values in association with sediments. chl a pGOP TP TPmax. TON TIN Figure 2. The proportion of taxa in sediment and epiphyton Assessing eutrophication impact from diatoms 70 assemblages showing no relation or a significant response to trophic 60 unimodal symmetric variables (HOF analyses of taxa with at least 10 occurences; p ≤ 0.05). Using indicator taxa. The first axis of a PCA with TP or 50 sediment epiphytes TPmax., TON and pGOP represents a compound impact

40 1.0 1.0 Table 3. Scores of selected impact 30 a. sediment b. epiphyton gradient (Figure 4, Table 3). Taxa can be ordered along this

% of taxa variables on the principal PCA axis 20 TP TPmax. and the variance explained by axis 1. gradient by means of detrended CCA, constrained to the 10 PCA scores, identifying the most reliable indicators (Figure 0 axis 1 score chl a pGOP TP TPmax. TON TIN 5). Impact can be inferred from their relative abundance. sediment epiphyton 70 TON TON Using calibration models. Assessing assemblage TP 0.75 - 60 unimodal skewed response to relevant proxies requires a robust relation. 50 sediment epiphytes TPmax. - 0.76 40 TON 0.94 0.94 Useful models were developed for pGOP from sediment 30 pGOP pGOP assemblages and for TPmax. using epiphytes (Figure 6). % of taxa pGOP 0.62 0.61

20

-1.0 -1.0 10 -0.6 1.0 -0.6 1.0 % var. 60.6 60.6 Model characteristics and assemblage composition allow to 0 Figure 4. PCA biplots of selected impact variables and assess the significance of inferred changes through time. chl a pGOP TP TPmax. TON TIN diatom samples from a. sediments and b. epiphyton. Figure 5. Species plots of DCCA analyses for sediment and epiphyton assemblages constrained to the summary PCA score

Figure 6. Calibration models for eutrophication variables: a. sediment assemblages, b. epiphyton. for eutrophication. Only taxa with at least 10 occurrences, a non-flat response and a weight of at least 5 % are shown. 5 pGOP (log10(x+2); mg/L) TPmax. (logx; µg/L) 4 a. sediment assemblages - PCA axis 1 score Craticula buderi b. epiphyton - PCA axis 1 score 3.0 4.0 a. b. Cocconeis placentula var. lineata method: WAinv. method: WA-PLS 3 Gomphonema pumilum r2 = 0.58 r2 = 0.64 jack. jack. Cocconeis pediculus Cocconeis placentula var. euglypta RMSEP = 13.7 % obs. range RMSEP = 14 % obs. range Cocconeis placentula Gomphonema minutum Eunotia minor 135 samples, 236 taxa 135 samples, 194 taxa Lemnicola hungarica Gomphonema olivaceum 2.5 Gomphonema subclavatum Gomphonema subclavatum Cyclostephanos dubius Nitzschia frustulum Gomphonema parvulum f. saprophilum Nitzschia amphibia Navicula tripunctata Nitzschia supralitorea Ulnaria ulna 3.0 Navicula capitatoradiata Navicula antonii Gomphonema acuminatum Gomphonema micropus Fragilaria fasciculata Planothidium lanceolatum Nitzschia paleacea Cocconeis placentula var. euglypta Gomphonema truncatum s.l. Fragilaria famelica Fragilaria gracilis Amphora pediculus Melosira varians Pinnularia viridiformis MT1 Nitzschia fonticola Cocconeis placentula Pinnularia subgibba increasing impact Stephanodiscus parvus Anomoeoneis sphaerophora Melosira varians Nitzschia dissipata Nitzschia palea var. debilis Surirella angusta Navicula trivialis Nitzschia amphibia 2.0 Navicula cincta, N. veneta Amphora copulata Achnanthidium minutissimum Navicula radiosa Gomhonema acuminatum Ulnaria ulna Cyclotella meneghiniana Nitzschia hungarica Nitzschia dissipata var. media Fragilaria capucina var. vaucheriae Eolimna subminuscula Caloneis bacillum Gomphonema parvulum

Nitzschia linearis Amphora veneta Nitzschia tryblionella Gomphonema gracile Gomphonema parvulum f. saprophilum observed observed Staurosira subsalina Stephanodiscus hantzschii Fragilaria capucina var. mesolepta Craticula cuspidata Cyclotella scaldensis Navicula gregaria Nitzschia linearis var. tenuis increasing impact Caloneis silicula Nitzschia palea Gyrosigma acuminatum Cyclotella meneghiniana 2.0 Navicula veneta Sellaphora pupula Eolimna minima Navicula slesvicensis Thalassiosira pseudonana Achnanthidium minutissimum Stephanodiscus hantzschii Cocconeis pediculus Amphora copulata Navicula trivialis Gomphonema minutum Nitzschia vermicularis Stephanodiscus parvus Achnanthidium jackii 1.5 Nitzschia acicularis Nitzschia dissipata pulchella Cyclostephanos dubius Cyclotella atomus Fragilaria gracilis Sellaphora pupula ag. Gomphonema clavatum Navicula cryptotenelloides Aulacoseira granulata Nitzschia recta Navicula antonii Cymatopleura solea var. apiculata Nitzschia rectirobusta Navicula reichardtiana Puncticulata radiosa Hippodonta hungarica Navicula rhynchotella Planothidium frequentissimum Placoneis elginensis s.l. Encyonopsis microcephala Navicula associata Amphora ovalis Staurosira mutabilis Asterionella formosa Navicula lundii Sellaphora seminulum Planothidium lanceolatum Parlibellus protracta Staurosira mutabilis 1.0 1.0 Navicula pseudoventralis Nitzschia archibaldii Planothidium rostratum Sellaphora joubaudii

1.0 1.5 2.0 2.5 3.0 1.0 2.0 3.0 4.0 Planothidium engelbrechtii Encyonopsis microcephala

-1 -1 estimated estimated -3 4 -2 4