Development of a spatially-explicit index of Chesapeake Bay

health

Michael Williams and Bill Dennison (UMCES)

Ben Longstaff (EcoCheck)

Roberto Llansó (Versar)

Claire Buchanan (ICPRB)

The Bay Health Index (BHI) is a spatially-explicit index that represents the major Bay habitats by using data from:

1) mid-channel surface (Secchi, chl-a, PIBI) and water column (DO),

2) benthic community (BIBI) and

3) peripheral shallow-water areas (SAV)

Secchi, chl-a, PIBI

DO

SAV

BIBI

Bay Health Index Methods

Compare to threshold levels

Chlorophyll a conc. Chlorophyll a conc. < thresholds

Frequency that sample values are below threshold levels (0-100%)

Water quality and biotic parameters combined into indices

Data integrated Compared to thresholds

Combined into indices

Water quality

Biotic

WQI

BI

BHI

Index values used to calculate report card grades

• 15 regions of the Bay

• Index: 0 to 100

• Grade: A to F

• Release in April

• www.eco-check.org

2006

BHI validation• Many water quality parameters respond to interannual

changes in flow and associated nutrient and sediment loading from urban and agricultural development in the watershed

• Therefore, indices used in the BHI should have distinct differences between low- (2002) & high- (2003) flow years and strong relationships with land use

Regional Water Quality Index vs Land Use (2000)

Year

r2

(n = 16)

Land use variable

r2

w/o York (n = 15)

Land use variable

r2

w/o York, SW tribs (n = 14)

Land use variable

1985 0.32 Dev 0.44 DevAgr 0.72 DevAgr 1986 0.24 Wet 0.29 Wet 0.29 Wet

1987 0.42 Dev 0.59 Dev 0.59 Dev

1988 0.42 Dev 0.52 Dev 0.49 Dev

1989 0.53 Dev 0.71 Dev 0.74 Dev 1990 0.50 Dev 0.58 Dev 0.81 DevAgr 1991 0.57 Dev 0.72 Dev 0.71 Dev

1992 0.61 Dev 0.66 Dev 0.69 Dev 1993 0.32 Dev 0.38 Dev 0.59 DevAgr 1994 0.42 For 0.43 For 0.73 DevAgr 1995 0.64 Dev 0.65 Dev 0.85 DevAgr 1996 0.37 Dev 0.38 Dev 0.80 DevAgr 1997 0.39 Dev 0.42 Dev 0.42 Dev

1998 0.18 For 0.22 For 0.50 DevAgr 1999 0.55 Dev 0.62 Dev 0.62 Dev

2000 0.24 DevAgr 0.31 DevAgr 0.62 DevAgr 2001 0.28 OW 0.32 For 0.70 DevAgr 2002 0.50 Dev 0.62 Dev 0.66 Dev 2003 0.30 Dev 0.30 Dev 0.63 DevAgr 2004 0.22 Dev 0.29 Dev 0.65 DevAgr 2005 0.24 For 0.23 For 0.51 DevAgr 2006 0.25 Dev 0.26 Dev 0.55 DevAgr

0

25

50

75

100

2.5 12.5 22.5 32.5 42.5 52.5 62.5 72.5 82.5 92.5 100

SAV

0

20

40

60

1986 1990 1994 1998 2002 2006

year

BH

I (%

of

10

0%

go

al)

No BIBI data until 1996

1996

• 4 regions w/o PIBI data throughout series & no SAV data for Elizabeth R. (NGZ)– Most of these represent very small area of Bay

• Range of BHI values is reasonable considering sustained high loading over this period and legacy effects– As loading is progressively reduced and the Bay’s

biogeochemical efficiency recovers, BHI values will increase

Concluding Remarks• We have developed an easy-to-understand, spatially-

explicit index that is robust and representative of the health conditions and status of major Chesapeake Bay habitats

• Work in progress and other health indices are being developed. Attempts to improve the BHI may involve:– Including higher trophic levels or other indicators (PCBs)– Altering thresholds– Augmenting monitoring efforts for some metrics (e.g., PIBI)

• With a doubling of the watershed population predicted to occur over the next decade, new methods of engaging the public and politicians are needed to hasten the implementation of BMPs and reduce nutrient loading

• The Bay Health Index and CB Report Card contribute to part of this effort by providing an annual, regional assessment of Chesapeake Bay health

Thanks to many of the Tidal Monitoring and Analysis Workgroup, and Living Resources

Analysis Workgroup members of the Chesapeake Bay Program