The effect of agricultural nutrient loading on estuarine bacterioplankton communities

Transcription

1 The effect of agricultural nutrient loading on estuarine bacterioplankton communities Jude Apple Horn Point Laboratory University of Maryland Center for Environmental Science Cambridge, Maryland

2 What is Microbial Ecology? Ecological Processes and Plankton Dynamics Paradigm Shifts Cultured vs. Non-cultured Bacterioplankton Dominance of Heterotrophic Processes Technological Advances Flow Cytometry Production and Respiration Measurements Molecular Techniques Where are we today? Empirical estimates of bacterial respiration Relative contribution among and within systems Diversity

3 Heterotrophic Bacterioplankton - Non-pathogenic! - Small ( 1µm) - Abundant (~10 6 cells/ml) - Comparable in biomass to PP - Nutrient & carbon remineralization - Drive water quality parameters (i.e. anoxia, nutrient availability) - Source vs. sink?

4 Cross-System View of Bacterioplankton bacterial abundance beta free-living bacteria alpha Archaea TSS POM nutrients RESUSPENSION CF gamma attached bacteria OLIGOTROPHIC OPEN OCEAN Depth SHALLOW TURBID ESTUARIES

5 Plankton Dynamics of Aquatic Systems PO 4 3- NH 4 + NO 3 - PHYTOPLANKTO N BACTERIA ZOOPLANKTON CO 2 NUTRIENTS

6 The Microbial Loop PO 4 3- NH 4 + NO 3 - PHYTOPLANKTO N HNFs BACTERIA DOM ZOOPLANKTON CILIATES MICROBIAL LOOP

7 Direct vs Indirect Effects of Nutrient Enrichment PO 4 3- NH 4 + NO 3 - ORGANIC MATTER LOADING PHYTOPLANKTO N SOURCE BACTERIA BACTERIAL GROWTH EFFICIENCY (BGE) ZOOPLANKTON SINK

8 Regulation of Growth PHYLOGENETIC Efficiency NUTRIENTS -C:N RATIOS - AVAILABILITY - NUTRIENT FORM SINGLE-CELL ACTIVITY - DNA CONTENT - ETS DOM - SOURCE - QUALITY - CONCENTRATION COMPOSITION Heterotrophic Bacterial Assemblage BGE = CARBON SOURCE PRODUCTION (BP) BP BP+BR RESPIRATION (BR) CARBON LOSS

9 Methods in Microbial Ecology Flow Cytometry Estimates of Bacterial Metabolism Production Respiration Bacterial Growth Efficiency

10 Microbial Lab Techniques: Flow Cytometry FLUORESCENCE & SIDE SCATTER DETECTORS COLLECTION TUBES FOR SORTING FORWARD SCATTER DETECTOR 480nm ARGON LASER SAMPLE INJECTION PORT CAROUSEL

11 Inside the Flow Cytometer SAMPLE INJECTION TUBE LASER SOURCE G O R SID E FW D DETECTOR ARRAY LDNA cells HDNA cells DATA INTERFAC E SORTING CRITERIA HDNA cells LDNA cells beads beads HIGH DNA WASTE LOW DNA

12 BP (grams C liter -1 hour -1 ) Estimating Bacterial Metabolism 1. Bacterial Production (BP) (BP) incorporation of 3 H- leucine 2. Bacterial Respiration (BR) 3. Bacterial Growth Efficiency (BGE) carbon conversion factor R 3 H 2 N C C OH H O 1 hour incubation SCINTILLATION COUNTER leucine incorporation rate

13 Estimating Microbial Metabolism 1. Bacterial Production (BP) 2. Bacterial Respiration (BR) O 2 consumption over time inlet mass spectrometry 3. Bacterial Growth Efficiency (BGE)

14 Estimating Microbial Metabolism 1. Bacterial Production (BP) 2. Bacterial Respiration (BR) O 2 consumption over time inlet mass spectrometry 3. Bacterial Growth Efficiency (BGE) mg O2 L y = x R 2 = RQ = 1 hours BR (grams C liter -1 hour -1 )

15 Estimating Microbial Metabolism 1. Bacterial Production (BP) BGE = BP BP + BR 2. Bacterial Respiration (BR) DOM 3. Bacterial Growth Efficiency (BGE) production divided by total carbon consumption BP BR

16 Objectives What is the effect of system-level nutrient enrichment on estuarine bacterioplankton communities? Today s Talk 1. Monie Bay as a natural experiment 2. Response of bacterioplankton to nutrient enrichment 3. Effect of salinity on mediating this response 4. Conclusions and Implications

17 Objective I: The natural experiment How do we evaluate the effect of nutrients on bacterioplankton? Small-scale nutrient enrichment experiments Large-scale field studies Caron et al Large-scale enrichments Impacted systems function as as natural experiments Cole Cochlan et al

18 Study Site: Monie Bay Research Reserve OPEN BAY SALINE CREEK S BRACKIS H CREEK

19 Little Monie (LM) Little Creek (LC) Monie Bay (OB)

20 MONIE CREEK (MC) 7ps u 23 % OPEN BAY (OB) 11ps u 10ps u 25 % <1 % LITTLE CREEK (LC) LITTLE MONIE CREEK (LM) 0 KM 2

21 Tidal Creek Nutrient Concentrations Agricultural Land Use 30 % ag ricu ltu re OB LC LM MC Phosphorus Nitrogen TDP (um) OB LC LM MC * * TDN (um ) OB LC LM MC * *

22 II Does the bacterioplankton community respond to nutrient enrichment? LM vs. LC

23 Bacterioplankton Response to Enrichment Bacterial Production Bacterial Respiration BP ( u g C/L/hr) OB LC LM * BR ( u g C/L/hr) OB LC LM Bacterial Growth Efficiency BGE (%) OB LC LM *

24 Single-Cell Activity in Response to Enrichment Bacterial Abundance c e lls /m l (10^7) * OB LC LM % C T C + c e lls Percent Highly-Active Cells OB LC LM * %HDNA Percent High DNA Cells OB LC LM *

25 III Does salinity mediate the response to nutrient enrichment? LM vs. MC

26 Community Response to Nutrient Enrichment There is a muted response to enrichment in Monie Creek µgc L -1 hr * BGE 0 0 OB LM MC BP BR TCC BGE

27 Single-Cell Response to Enrichment The proportion of highly-active cells is higher in Monie Creek, suggesting compositional differences in the assemblages % CTC+ cells % HDNA cells 0 OB LM MC 0 %CTC+ %HDNA

28 What mediates the response to nutrients? Shifts in phylogenetic composition? DOM quality? Transplant Experiment Optical Characteristics of DOM DOM Lability

29 Transplant Experiment 1. Collect water, filter, and fill dialysis bags 2. Transplant dialysis bags 3. Transplant control bags 4. Harvest bags daily 5. Measure BA, BP, and single-cell activity MONIE CREEK WATER LITTLE MONIE LITTLE MONIE CREEK WATER MONIE CREEK

30 Transplant Experiment: Results BP (µgc L -1 hr -1 ) BP ( g C L -1 hr -1 ) FW in SW SW in FW 0 initial day 1 day 2 day 3 SW in SW FW in FW SW in FW FW in SW

31 Optical Characteristics of DOM absorbance Are there differences in substrate quality, as evidenced by CDOM? 1. CDOM is an index of refractory, terrestrially derived organic matter 2. Absorption (A) spectra from nm 3. Calculate absorbance (a λ ) and specific absorbance (a 350 *) = 0.45a 350 /[DOC] 0.4 y = 29.46e x 0.35 a R 2 = y = e x R 2 = nanometers MC OB A comparison of the absorbance of water from MC and the open bay.

32 CDOM and DOM Quality? Monie Creek is enriched with DOC and CDOM DOC (mg L -1 ) R 2 = 0.61 p< specific absorbance a R 2 = 0.79 p< salinity OB LM MC

33 DOM Lability Experiment 1. Collect water µm filter 2L 3. Inoculate with resident bacterioplankton 4. Incubate for 4 weeks 5. Measure DOC

34 DOM Lability Experiment: Results Calculate DOC in µgc L -1 day -1 (i.e. lability) and percent labile DOC = (day) R 2 = 0.96 p < DOC (mg L -1 ) day of incubation

35 Regrowth Experiment: Results DOC consumption (ugc L -1 day -1 ) or percent total DOC consumed DOC consumption percent consumed

36 Conclusions I. Monie Bay as a Natural Experiment II. Effect of nutrient enrichment? Positive Response on Community and Cellular levels. III. Effect of Salinity? Freshwater systems have lower DOM Quality IV. Relevance and Implications? Source and Sink Indices of Eutrophication and Management implications Monie Bay is a Model Estuarine System

37 2 logbp = *logCHLA R 2 = 0.23 p < log10(bp (µgc l h )) log 10(chlorophyll-a (µg l -1 ))

38